Just pretend they say +1; They are the same thing basically.
Sell them for the same price as other HQ's.
Give them out to your crafters in your LS to make +1 gear for you.
Use them yourself.
Drop them.
NPC them.

Lot's of answers to this problem you're having with -choosing- to hold onto out of date items. As far as I am aware from mining/some botany; You can't obtain +3 items any more and I haven't seen them drop in a while either so I can assume mobs don't drop them at this point. You obviously can't craft +3 so the only answer is that they no longer exist in the game other than what people are willingly holding onto. Might as well make use of them and get them out of your inventory/the game rather than fretting over the +3 rather than +1 issue.