G,
Did some checking on the inventory we have and we only have 1 of the BFG TA radials. 2 years ago when I bought my BFG's I waited over 3 months for us to get them in. At that time I wasnt working for them but I called every week as they were back ordered. They continue to be on back order all the time due to less manufacturing time as I explained earlier. I didnt have time to check on the Firestone tire as we don't sell many of them and they are supplied to us thru an outside vender. I will try to check tomorrow to see if anything is available. Other tires that are that size that we carry would be in the Hankook line. The MIleage Plus II are advertized at 80K miles with UTQG of 620 A/B. (UTQG stands for Uniform Tire Quality Grading) (The 620 is the tread wear, first letter being Traction rating, 2nd letter being temperture rating) The 2nd Hankook is the Optima 724 listed at 70K miles with the UTQG of 500 A/B and the last Hankook is a Dynapro AS which has a UTQG of 440 A/B. Also has ROWL.(raised outline white letter) Another tire we stock in that size is the Uniroyal  Cross Country Tour that has a UTQG of 540 A/B. ROWL.
This the the problem with the 15" tires. I am sure that their are other tires in other brands that are out there that we dont carry, however I have access to 15 different brands and thats all I have available. If you want the vette to stay as stock/original you can have a local tire shop order you tires and wait until they come in if your not in a hurry. Other option is to go to 17" or 18" wheels but your expense goes up because of wheel purchase. The tires actually are not that much more expensive and some are actually less. A much wider range of selection and they will be available much longer.
Best of luck.
Rodney