One answer is yes; I personally remember seeing it for sale at a Radio Shack store in Texas or California. In fact, I almost bought one. The Jupiter Ace was a British computer with the Forth language in ROM. It was developed by Jupiter Contab and marketed beginning in 1982. The Jupiter Ace 4000 was a model for the American market, but the only difference seems to be a slightly more robust plastic case.
It did not sell well, and only 800 Ace 4000s were ever made (5000 of the original British version were built). One reason for this is that it had only 1 kbyte of user RAM. There was separate RAM for video. (I know Forth is space-efficient, but only 1000 bytes to do anything?!) Memory could be expanded, which would double the price of the computer.
Back to my "yes". I saw it at Radio Shack. However I can find no evidence that Radio Shack ever marketed it, though. So perhaps I happened upon a store which chose to buy some and sell them on its own. The official American distributor was:
Computer Distribution Associates
Jupiter* Computer Division
56 South 3rd Street
Oxford, Pennsylvania, 19363, USA
That information came from the Jupiter Ace 4000 Forth Programming Manual by Steve Vickers. A PDF file for the book is available on the web.
I don't actually remember where I saw it. But I can do some deduction. According to the Wikipedia, the Ace 4000 began being distributed in 1983. From 1982 to 1985 I attended college at Abilene Christian University in Abilene, Texas. During that time I lived in both Abilene and Midland. So it is extremely likely I saw it at a Radio Shack in one of those two cities. After being graduated (Dec.85) I moved to San Rafael, CA, so there is a minor possibility it was a store in or near there.
Does anyone know if Tandy Radio Shack ever officially marketed these computers?