I had a heck of a time with motivation myself but I learned trumpet for/ with my son and it is what has kept me going.
But I am surprised you can't find any local bands to play with. Where I am in NJ there are always opportunities to join bands- in the town we have a community band, a Dixieland band and a jazz/ big band group (which I am in). All are looking for trumpet players from 4th chair up to 1st. Sure they aren't paying gigs but if you just want to have fun and play with guys the opportunities should be there.