Weapons with 1000+ power is 100% impossible to obtain.

Seems as to what it is, there is no way to get any weapons that is 1000+-3000+ power. There really isn't. I believe Sega banned me from getting stronger with weapons.

Can't you just get one of the Millionaire or the Croesus weapons from the Collection Trader near the quest counter in the base PSO2 ? At least just as a starting point. The base attack for those is already like 1.5k+.

I'm pretty sure Weapon Badge 5 are still given out, so you should be able to save those for some high end weapons as well.