any f1.4 DX lens available?

I guess there is none...still love my D500 but envy the Z mount now has three Sigma DX primes at 1.4

Literally any f1.4 F-mount lens, any brand, with autofocus will work perfectly on your D500. There is no need for the lens to be DX specific.

Not sure about DX specific, but certainly lots of f1.4 primes that are great with the D500. I only have a Nikon 50mm f1.4 and a Sigma 30mm f1.4, but they are great on DX nikons and there are lots of others.

I admit to not being particularly well-versed in 3rd party lenses, but Nikon never really beefed up the high-end/pro DX line. Even in the pre-D3 era they still regularly introduced new FX designs(although some were pretty obviously designed with DX in mind, like the first gen 70-200 f/2.8G VR that's super sharp basically over the DX area when wide open but with soft corners on FX).

There are probably some I'm not thinking of, but in all honesty the only DX primes I'm thinking of are the fisheye(10.5mm?) and the 35mm f/1.8. The latter is a wonderful lens, but its build quality fits its $200 price.

As said, though, stick any FX f/1.4 on and you'll be fine. There are bunches of them, whether AF or MF. Yes, they are larger than purpose built DX lenses but still work fine. Many are actually great on DX bodies as field curvature can really show itself on large aperture lenses and a DX sensor cuts off the worst of it.