Depending on your taste ... I have found www.corvettemods.com
the most decent and reliable and have personally tested their ordering, delivery & after-sales support.
A tremendous thanks to @ddgermann for the referral to this resource as he has experience with
many of the not-so-great resources - you may chose to PM him privately to ask if he has experience with
any particular supplier that you are thinking of.
Most of the engine dress up mods come from American Car Crafts. I have spent quite of bit on engine dress up mods this winter and will be installing in the new year.