DLC's in Halo Reach came with some new achievements. As the game became less popular and currently there are no dedicated queue lists to play only on the new maps, some of the achievements became really difficult to get as some of them require that DLC maps.
Usually, when playing on matchmaking, you never get that maps to vote as all the players must have the DLCs in order to get the possibility to play them, and the few moments when that strange thing happens, no one votes the new maps so you can't try to get the achievements. What it's more, even if you manage to play in a new map, you need to do the thing the achievement requires.
I recently discovered that I have only 4 achievements left to "complete" the game, all DLC multiplayer ones.
How can I increase the possibilities of playing in a new map? Can I create a custom online map with friends to get them?