It depends on what you need, really -- and, of course, on where you are.
As others have pointed out, the CMOS version of the 6502, the 65C02, is still readily available. Western Design Center sell them through their distributors, notably Mouser, who ship worldwide. There are, however, minor functional differences between the 6502 and the 65C02. If your application relies on undocumented opcodes, or makes creative use of certain bugs in the 6502, the 65C02 may not work for you.
On the hardware side, three pins have been re-assigned in the WDC 65C02, compared to the 6502 and earlier (Rockwell) 65C02s. You need to ensure that VPB (pin 1) and MLB (pin 5) are not connected (pin 1 is usually tied to GND in older systems) and that BE (pin 36) is tied high.1
Also, the current WDC datasheet for the 65C02 gives V_IH,min (i.e., the minimum input voltage guaranteed to be recognized as "high") as VCC x 0.7, i.e., 3.5V in a 5V system, whereas NMOS or TTL ICs only guarantee a minimum of somewhere between 2.4V and 2.7V on high outputs. This means that the current WDC 65C02 may not work, or may show intermittent faults, in old NMOS / TTL circuits, even though past 65C02s have performed quite well in these circumstances.
These last two issues may be resolved with an adapter board.
That being said, unless you already know it will not work, I would try a 65C02 first.
If indeed you do need a 6502 (without the C) for testing, I see four options for you:
Your best bet to acquire a known good chip is probably to buy a working machine that contains a socketed 6502, so that you can then test this 6502 in situ pefore proceeding.
You can also look through internet forums (with users from your corner of the world) that deal with 6502s and 6502 machines. Some have market places where people sell tested 6502s; these tend to be more reliable than eBay.
If you feel lucky, there are many sellers on eBay and Aliexpress who peddle (ha!) 6502s, but these are often untested, relabeled and/or of dubious origin. They are also cheap -- if you have a known good machine to test them in, or can get your hands on one, you can buy a handful and see if they work. Some probably will. On the other hand, if you had a known good machine, you probably wouldn't be asking here.
Finally, there are so-called chip brokers who specialize in sourcing new old stock ICs. A quick check with one here in Germany show that they claim to be able to source several thousand NOS MOS and CSG 6502s. Chip brokers usually don't deal in single quantities, but sometimes, someone organizes a group buy on one of the abovementioned forums.
1 Incorporating a commment from cjs.