Well shit. 5,000 psi gas cylinders do exist but you won't find them in smaller sizes.
You want what we call in the industry as a "sample bomb". Hoke, and Autoclave Engineers, Swagelok, etc. make small spun cylinders with that pressure raring but they will be $$ amd I don't know of a gas vendor that will fill them.
Here are some to give you an idea.
https://favfittings.com/sampling-cylinders/5000 psi cylinders will be k size and larger and will be lease only from a vendor.
Now what are doing with this? What is your working fluid? (Ar, He, N2... I assume this is gas service).
If you want a small volume device at that pressure you will have to pressurize it yourself with a pump from a k bottle.