I've lost the tiny spring for the firing pin block. Taurus says I have to send the gun in to get the spring replaced. I know what the part does, but what possible failures if I leave it out? Drop firing?

Maybe this video of a TX22 trigger will help you?

I wonder if a small spring from a more common pistol might fit.  Glock, S&W M&P, maybe a Series 80 Colt?   Advantage Arms 22 conversions use a firing pin block might be worth looking at their website for a spring kit.    Brownell’s has schematics for many pistol and pictures of parts.  


Here is a link to the Advantage Arms Parts.

http://www.advantagearms.com/mm5/merchant.mvc?Screen=PROD&Product_Code=GlkSafetySpring

Thank you. But it's really hard to get a sense of size from pictures. The spring I'm looking for is maybe 1/8" diameter, 3/16" long.

I happen to be looking at a spring that's roughly that diameter but a bit longer, from a watch band spring pin that blew its guts out on me yesterday.  Grab an old watch from the junk drawer, yank the pins apart and trim the spring?