Does anyone know if stock style steel rims are available in 17" and 18" sizes? I would like to use stock dog dish hub caps on this size of rim to make a T/A clone/style Challenger.
Plain steel rims, yes, Rallye of magnum style in steel, no. Stockton has made 17" steel wheels that are factory appearing, hence can use dog dish hubcaps. However, be advised they are not lightweights and will likely come in between 35-40 pounds each. That can be a significant detriment to performance both in a straight line and with handling.
I like the look of the stock caps and rims but you can't find good performing rubber in 15"
There is still good performing 15" rubber out there, it just isn't easy to find and not cheap when you do find it. For example, Avon 295/50xVR15 with a an A rated traction tread at around $300 each. More reasonable compromise may be the M/T S/R with H speed rating and a new tread design for around $150 each. With the weight your going to be gaining with 17" steel wheels, you may actually be performance ahead using lighter wheels and lesser quality 15" rubber.