why dont you rebuild it yourself?its easy to do.a kit cost something like $65 from a corvette parts place called ZIP.it says you need a small shop press but a nice vise will work just fine.
it will cost you $20-$25 for shipping alone if you send it to someone.
here is a kit for a 427 the same year 1968.this should be the same.
http://www.zip-products.com/Zip/productr...770B263295F4A5E