here you go...Compomotive...15x8 (plus some in 16" size)
Those cheap american racing Empi-wannabes are known to crack as is without fooling around with them
I wouldn't trust them any wider than they already are, you'd put even more stress on the center section
You can also get brand new Revolution wheels for our 914s in the correct 4x130 bolt pattern...this is what I did, I like the idea of running brand new never been beaten on wheels instead of "who-knows-how-they've-been-treated-30-year-old-rims"
oh yea, last time I checked into having rims widened, the cost was ~150 each with a lead time of a few weeks to a month