I mount my own a company in Korea, Malin, makes all the sizes for medium format ( 645, 6x6, 6x7) they also sell a little film cutter that works for 35mm and roll film. I'm sure there's someone left that mounts. I like to shoot Fujichrome every fall. The slides are stunning.
I've only used the 35mm but they're hinged and close with a friction fit. I just used the mounts, a pair of scissors and a tablet as a light box. I'll post some photos in a bit.
You can see the little pins and holes which hold it closed with friction. The negative slides into the hinge a bit so it's not just floating around before you close it.
They are a firm all-round press-fit, but disassembly if and when required, is a fraught process — so much so that due to my frequent print-runs I was forever mounting/dismounting with the transparencies flinging themselves across the room! As a result of those experiences, I no longer use any slide mounts, preferring archival polypropylene card mounts and sleeves (also available from Vanbar Fitzroy).