Huh? Where'd you hear that? Unless your mental illness has involved a reportable event, such as involuntary commitment or an adjudication of mental incompetence, there's no record of it, and you can still get a gun legally. There are various legislative proposals all the time to change that, and perhaps a few states have succeeded in imposing a few more restrictions than federal law, but generally speaking "mental illness" is no barrier to buying a gun.
Sorry I live in NJ... we have to sign a release waiver. I just assumed that other states would have similar documents.