If I could not get an AR, AK, etc and wanted a defensive gun I would look into a lever gun or the a Remington 7615.
The 7615 is a pump action that takes AR magazines. I haven't looked to seriously into these guns. As such I cannot say if it is what I would choose in the end but I would give it a hard look.
The other option I would look at is a lever gun that was set up for this purpose. A bse lever gun can be had NIB for under $500. I would add a red dot, sling, and as with any defensive long gun, a light. One could debate calibers. In reality everything from pistol calibers to big bores like the 45/70 could be useful and have their advantages and trade offs. I'd look hard at a 30-30 which would give performance similar to 7.62x39. It does, however, have a limited capacity. A 20" barreled gun likely will hold 6(+1), a 16" gun loses a round. Whereas a similar 20" gun in .357 mag tends to hold 10(+1). A .357 mag out of a 20" barrel almost approaches "real" rifle power. Depending on uses the .357 mag may be a better choice.
A lever gun can be run like a hybrid between a shotgun and rifle. Its like a shotgun in shooting and loading and trying to keeping it topped off.
A nice thing about getting a lever gun is that you'd have a gun worth owning even if you latter could get an AR, etc.
Here are some defensive lever guns:
View attachment 648172
View attachment 648173
I like the rail with the micro aimpoint and an offset surefire. It similar to how I like an AK set up.
View attachment 648174
I'd prefer this to ammo on the stock. It is faster to get at and load. It also doesn't interfere with switching shoulders like an ammo holder on the stock could.
A side saddle I saw once, not sure if it is widely available.
View attachment 648175