The suggested gear rating for lvl 55 HM's is 148, and the best you can do by running lvl 50 HM's is lvl 146 gear. The lvl 55 HM's drop 148 gear mostly and some 162 gear. How in the heck can you get 148 gear unless you run ops and/or grind for basic comms which are good for 156 gear? This is a flaw. Ideally lvl 50 hm's should drop 148 gear and the lvl 55 HM's should drop 55 gear exclusively and set it up so the basic comms can be used for lvl 162, and vice versa. The point being that lvl 50 hm's should help you get geared for lvl 55 hm's and lvl 55 hm's should help you get geared for lvl 55 ops. This current system is pretty gd dumb.
1/ If you done full makeb including dailies you should of acquired enough comms for at least 2-3 pieces, section x also rewards basic comms and is very quick to complete.
2/ While the level 50 flashpoints/OP's don't drop 55 gear inside, they do reward basic comms for completion of the group finder daily.
3/ Also EV/KP HM drop hazmat which is 150 rated and EC HM/NiM Dread Guard which is the same rating but with set bonus. There are loads of groups doing the classic ops weekly especially EV/KP HM which are the easiest and only require 136 rated gear, and you only really need one tank for EV so grouping is faster.
4/ You're also forgetting crafters and the GTN, the mods for 66 both blues and purples are real cheap at least on my server. You only need to spend a few hundred K to get a full set of purples or as little as a couple of K for a blue 148 mod, or if you prefer crafting the schematics are available from the crafting trainers.
There's really no excuse, however bioware are adding new role-less story mode flashpoints in 2.3 which drop 66 blue gear and are very easy. For now though I'd recommend grinding a few dailies for basic comms, playing a bit of EV/KP HM for some hazmat and checking out the GTN for mods.