If your character has the credits and the patience to seek out a dealer, older military grade models can still be found on the shadow market for about the same price you might pay for a brand new military grade model (whose sales are closely monitored and restricted to Imperial agencies). That means they would probably run you about 2.5 million credits, which still isn't too bad all things considered.
Now, you could probably get a basic, demilitarized version legally from a certified MandalHypernautics dealer, but you would have to have valid credentials and a relatively clean record.
You would also have to pay for any upgrades yourself and arming it up to milspec would be highly illegal. MandalHypernautics offers a great warranty program on certified pre-owned starships, but lawlessness and rebellion aren't covered under it, unfortunately.