new sights for 317 / 442 pro question

[M66 3"]

Greetings all,
A few years ago I picked up a 3" 317 8 shot. It looked really cool and has always functioned well with the exception of one thing- I can't hit anything with it. The worn cylinder ring attests to my faithful efforts at learning, but targets at any range short of point blank are pretty safe. I've tried to replace the rear sight blade, but the sample I had on hand did not fit. My questions are; 1. Is there are readily available replacement and 2. I understand the fiber optic rationale, but "V" notch with round front doesn't work well for me, square/square is what I'm after. Also, in an effort not to clog the forum- What are the primary differences between the 442 production model and the 442 "Pro series"? I understand the Pro is cut for moon clips, and the specimens I've seen are w/o the internal lock. Anything else? I'm in the market for a 442, have no use for moonclips but prefer a "sans lock" model. Any guidance or leads on this? Thank you in advance.