The trading community is very resistant to new currencies. You can't really force that short of making 3 stamps craftable into a key or something equally drastic.
For starters:
1) The current trade filters are terrible. They don't track kills on a particular map, they make ALL your kills with that strange track on JUST that map. These need to work like a traditional strange part. For example, "Coldfront kills: 5, Frontier kills: 23", not effectively ruining your strange for all other maps.
2) Stamps need to do something. For example, buy a stamp for a map, and for the next 24 hours on that map (and only that map), your droprate increases. Or have them be an actual item in the backpack, and apply it to a crate to increase the unusual unbox rate by 1% (one time) if unboxed on that map.
3) Special "event" crates for all custom maps. Let the map creator(s) pick up to five items from the workshop to go in the crate (pending Valve approval of course), and have them ONLY drop on that map. The crate can be a standard template with a treasure map nailed to it, maybe even the map's stamp image on it. Have the crates give a chance of giving strange cosmetics and generation 1 unusuals.
Unfortunately relies a bit heavily on modelers, but at least by letting the mapper(s) pick the items, they could pick cosmetics that fit the theme of the map, pick ones made by the mapper(s), or have new models made with the mapper(s) as co-authors. Or at the very least, ensure that items in it give a share to tf2maps. It also makes a new map a mini-event.