midsidenode given your intention of staying vague it's difficult being much help.
You say noforn, which I assume means no foreign but you don't actually state a country you're in. Given the 3 big companies you list then I'd guess you are US.
Relatively few companies these days have the facilities to do everything you list internally, however many have experience managing the process and getting in external expertise/faciliites as required.
If you could clarify whether this is military or civilian that would help.
For military the classic way to get a quick pod onto an A/C is to take a fuel tank and cut the required holes etc in it.
For civilian given most don't have any kind of pylon you also need to be looking at modifying the aircraft.
I interviewed at this place a few years back (they could't take me as being from UK originally I couldn't get clearnance) it may be up their alley.
They weren't very big when I was there but I don't know if they've grown since. Plus for the type of thing you seem to be talking about size isn't everything.
who I think you're already familiar with will be a strong contendor for a military pod. Simplistically they may be able to modify one of their cargo/luggage pods (toward th end of the page.
Not a US company but has done work gor USAF etc
Portsmouth aviation has also done work for USAF
I used to work there, they have some good guys, if you're remotely interested I might be able to get one of them to look at this site.
Any company that makes bomb racks, pylons etc may be able to help. Examples would be
Maybe
can help.
To give more specific help you really need to throw us a bone, is it some kind of sensor pod? If so does it need a big GRP or 'Glass' window? What type of A/C, or at least general performance all that good stuff.
KENAT, probably the least qualified checker you'll ever meet...