I bought all my bolts at autozone and I also took some old O2 sensors made my own extensions cut and spliced the wires to a new sensor and it cost me about $15
When I did mine I used stainless steel allen head bolts, you can get em at any good fastner supply outfit or McMaster Carr. Johnny's right about splicing in wire from used O2 sensors, you'll find that the O2 sensor wire is stainless steel, at least it was on mine. Good luck, 91 ZR1 #2039
If GM don't have em you might try Kurt White aka Limey. I got mine from him because GM was out of em, said they were not discontinued but didn't know when they would do another run on em. Good luck, 91 ZR1 #2039
The bolt heads are 10mm don't remember shank diameter or thread pitch. When it comes to the metrics I just take em to the fastener store with me, I'm still kinda dumb about metric thread pitches. 91 ZR1
did place an order online here http://www.zr1products.com/products.html havent got a response yet didnt have time to call today hope the kit is still produced? if not i think i can buy the bolts here and could make the extended oxygen sensor adaptors. kinda bummed stainless works was out of stock with the headers and x-pipe said it may be 2 weeks until they ship oh well guess i will have to wait...