Hi, I have found a number of aftermarket suppliers of V-8 timing covers...
Since I have read a number of posts here and there that new covers are not as good as NOS ones... something to do with alignment. Since I have not had any issues with old used ones, I find shelling out $200.00 on new aftermarkets to test with not worth while.

Most issues I have found are due to the installation process... If one installed the cover without the use of a AMC Tech manual, you can kiss your distributor drive gears goodbye.

I learned this back in the 80's while in school my first car was a 304 Grimmie
I had bought. It had a front end oil leak and the mechanic who fixed it said it would need a new timing cover gasket. After 1,000 miles my distributor drive gears failed... and I ended up doing the whole thing my self. Since then I have found so many back yard AMC'rs ending up having to do it again or sending it in to a mechanic.

Used distributor drive gears and covers can work without any problems just make sure they are not worn out. So it seems that from what I have seen and read that many have not installed a timing cover properly and have given false information in regards to it.