Another thought is to just fabricate your own. It really isn't that difficult and the parts are readily available. As an example, when I owned my Lone Star, I used merge collectors from Hooker, Howe racing mufflers and some end pieces I bought off the internet. I subsequently did the same thing with my Superformance and performance gains on both applications were excellent. Both the Lone Star and SPF side pipes are rather restrictive. If you do a search here there have been several threads on the subject.
On my SPF I gained dyno verified 60 RWHP and 50 RWTQ after going to larger headers and Side pipes. The more c.i.'s you have the bigger the gains by providing better breathing, and FE's really need to breath.
Here's a shot of the pipes I built for my SPF:
The Lone Star's looked very similar except they were ceramic coated silver.
