Run strikes I'm drowning in fusion rifles

Go to the gunsmith every so often. He sometimes has rare fusion rifles, which you can keep buying until you dismembered enough for your bounty.

Wait for Banshee to get one, buy 10. Glimmer isn't used for much else.

I had the same issue. Took me nearly three weeks to get all 10 Rare+ FRs. This was prior to the patch of 'The Cave', and prior to the "fix" for the Cryptarch. I ended up getting what was needed from running a plethora of Strike missions, lucky for me I got the Juju Exotic bounty that requires 25 Strike mission completions. I would say your best bet is to chain run strike missions, work your bounties while doing them when you can.

loot cave. LOL. Sorry, had to. I had way too many of those things back in the day.

Yeah I've been checking him. No luck yet.

i got the bounty and bought 3 before the gunsmith changed his stock out...didn't know about 10 fusions before getting the bounty :/