[Preface: The question misses to restrict it to electronic computer equipment, as I assume that#s what you're after. 80 column punch cards were already a thing before and there was much competition]
Well, the story of compatilbe punch card equipment predates mainframes by far. In fact, The 80 column rectangular hole punch card was in part developed to shake of competition. For next to all prior designs (22x8, 24x10, 45x12) competitors did build compatible machinery, foremost data entry devices, but anything else as well.
In the mid 1920s IBM wanted to increase data density once more, but this time with an additional goal of making it in a way that allowed patenting it. That's were the 80x12 with rectangular holes came into play - them being the patent worthy part Watson Sr. wanted to keep competition away (*1).
The patent got awarded in 1928, thus valid until 1946
Remington Rand, at that time eventually the biggest competitor to IBM of course had to counter this. They kept the 45x12 card with round holes, but changed encoding, storing two characters in one column, so it was called the 90 column card.
Other manufacturers developed similar formats with up to 130 characters per card - all with compatibility to the 45x12 card.
IBM tried very hard to corner that market, for example their tabulating machinery was rented out with the obligation to only use IBM supplied cards. At some point they made more than 1/3rd of their business in selling paper, not machinery. All based around that patent. This came to an end in the mid 1930s, when the US government sued IBM to open up the card market. From that point on only card punches making square holes were the only devices were they could keep competition away. This means keypunches, as well as duplicators and interpreting punches.
What was the first company other than IBM, to sell a reader that could read IBM format eighty column punchcards?
Now, readers there were plenty, as reading wasn't protected by the 1928 patent. Only punching square holes :))
when it's about computers, the first legally to do so would be again Remington Rand. When they unveiled their UNIVAC, they had a great advantage over IBM, so IBM was keen to get some licences - and Remington Rand did want a licence for square holes since the 1928, so they exchanged patents. A great deal for IBM, no so great for Remington Rand - but who would have guessed back then that punch cards soon would loos being the most important part in data processing.
Since the UNIVAC was tape based (seriously ahead of it's time in using magnetic media), but users wanted to combine the computing power with their punced data stacks, a pair of card to tape and tape to card converters were the first products. These were stand alone machines. The idea of direct connected peripherals was still in the making. Being able to operate them independant of the main computer was quite preferable.
Now, as we all know, when Remington Rand became Sperry, several members of the ERA/UNIVAC team became soon disenfranchised, left and formed CDC in 1957(?). CDC started business by building quite successful magnetic drum memories. Next was a tape device, followed by card readers and punches - the famous 405/415 - followed by printers. The card devices were 80x12 IBM card compatible (*2). While their CDC 1604 mad a big intro in 1960 - and layed ground for many to follow, CDC was already in the mid 1960s a major player in peripherals. Right at the time the /360 was introduced.
As I understand it, the industry of IBM plug compatible peripherals didn't really take off until the late sixties, but I would be interested to know whether compatible punchcard readers existed earlier than that.
The whole plug compatible business only became a thing after the introduction of the /360 in 1964. At that time the patents were gone for good and next to every mainframe or mid size computer manufacturer offered readers and punches. A great number of them using OEMed CDC devices. In fact, CDC was so early - and willing to deliver - that only very few tried to build their own devices. Instead these companies focused on their computers and just bought CDC punch equipment (and drives and printers ...).
The only other company that made a larger inroad with punch cards - and here only for readers - was Documation. Their readers targeted the lower end, were CDC didn't supply anything, with very compact desktop models. They became kind of standard for minis with a need to read IBM stacks.
Long story short:
- If it's about the 80 column catd in general, look into tabulating machines of the 1930s.
- If it's about electronic computers, look at Remington Rand/Sperry
- If it's about peripherals, then CDC is what you're looking for.
*1 - Funny twist here, for the new, high density 96 column format, introduced in the 1960s, IBM switched back to round holes - making them rectangular wasn't as great of a choice as IBM did promote it in the 1930s :))
*2 - There is also a story about them trying to circumvent the IBM patents (as Sperry, not CDC was a licencee of IBM) with oval holes, until they realized they could do it anyway.
