I want to homebrew a circular polarized crossed dipole and would like to have it on an NMO Mount. I know people make nmo to N adapters which is what I’m currently looking at but was wondering if anyone actually made a NMO antenna base.

There are zillions of antenna bases that fit onto NMO mounts, that's the whole point of the NMO mount.

I don't think I've seen any DIY NMO sockets, adapters like https://www.amazon.com/TRAM-1295-NMO-Adaptor-Antenna/dp/B010MAVD6M are probably your best bet.

Alternatively you could use a simple 1/4W vertical antenna and steal the base from it, since it's just set screws that clamp down on the wire.

I have one that I could donate if you need it

I've done a little with circular polarized antennas, I'm curious what you are looking to do, there might be some alternatives for you.

It’s for satcom. Both the noaa and mil birds.

As of now I am thinking of just using a N type adapter

You might take a look at the skew planar wheel antenna. The feed arrangement is easier and it has better circularity throughout the signal pattern. It does have a pattern null straight overhead, but LEO satellites spend very little time there vs lower and middle elevation angles. A turnstile has good performance on-axis, but as an unsteered mobile antenna would have poor circularity and signal strength at lower elevation angles. For geosynchronous satellites that is less of an issue.

http://www.ve3byt.com/SkewPlanarAntenna/

http://vk6ysf.com/skew_planar_wheel_antenna.htm

For homebrew construction it would seem pretty feasible to build such an antenna onto a 1/4 wave threaded stud NMO base (like this) or an NMO 3/8" mount base (like this).

I'm not sure what the pattern would look like over a ground plane

For ~250MHz milsat a SPW would be nearly 2 feet in diameter though .  And if you're talking about 130MHz NOAA WX satellite downlinks, that would be... large - over 3 feet diameter.

If you had a big flat vehicle roof on a trailer or something like that you could make patch antennas.