Call me skeptical, but if this stuff exists, it's been moved to another location already. A congressman isn't going to show up to some base and be given access to the hanger with the UFO in it.
Sounds like an urban legend to me. This guy supposedly knows "exactly where it is" yet isn't willing to reveal the location, except it is "outside the US." Has he seen it? Nope. Let me guess: even if you go to the building, you won't be able to find anything because it's in some secret below ground level a normal person can't access.
That’s why congress needs to send a special envoy to investigate, and from what I’ve read they are looking into doing so. Ross Coulthart likely did not get this information from David Grusch btw.