BEEN through this a few times 20 years ago pyrotech racing suits sold me thread & some material but they really didn't want to you can call to try.. years later i found a auto upholstery shop to help me out they have the heavy duty thread, but not fire retardant , you don't need it...
go to [ ad huntr .com ] or [ craigslist search all ] there the same thing, this will let you search the hole USA,, at once.then type in what your looking for,,,, example . simpson fire suit or sparco fire suit or bell fire suit...... there is always suits on there or anything else...