Get what you can now. Stock up on spare parts, extra magazines and ammunition, sight the thing in and let it sit for when you need it. if you advertise owning such a gun you will simply stand out more and make yourself an easier target for confiscation.
And get a good gun, one that is solid and reliable from the start, and forget about 5 year warranties. Have you forgotten that one tenet of gun control, that has already been passed, is to require every gunsmith to list and identify any firearm brought for service???
So yeah, you have had it for years and maybe nobody knows about it and maybe the paperwork that had to be completed has been destroyed and maybe nobody knows about it but, if you bring it in for service somewhere they will register that the firearm was brought in for service and who owns it.
The thing to do is buy on the private market and stash it. JMTCW.