I have run into these problems you describe but I don't think it's a flawed or bias system. I think what's happening is the lower level stuff is more popular on the gtn than the 50 stuff. Level 50's generally aren't buying gear through the gtn, they're using pvp/pve comms for gear. The low level stuff, everyone wants. There are some days where there is just no resolve mods/armorings at all and other days where that's all that's available. Sometimes it changes within the hour depending on who's online and crafting/listing their items. Sometimes all it takes is going into a 15 minute wz and by the time I'm done there are 5 resolve (or whatever) armorings listed where there was none 15 minutes prior.
I think it just boils down to luck of the draw, time of day and who's listing/looking at that time.
Hehe a few times I've been ninja'ed as well. You know, when you purchase an item and a new mail pops up. Then when you go to retrieve it, the mail has a refund of your money with some dear john letter that states "the item was already sold". Someone else way buying it at the same time (or seconds before you).
I just tried the advice given. I entered item modification, armoring, any, Tharan Cedrax, cunning, 1 thru 35. I got NOTHING. My Smuggler, level 50, found 4 pages of stuff. What gives?
Actually I have found the 'search items for (companion name)' to not work properly. Or I should say I have never figured out how to do this correctly. I always get blanks as well. What you should do is search armorings within a level range, something like 29-33 blue and better. You can do the same with all items listed. No need to see stuff way under or over your level. But yes, I found searching gear that usable for X companion flawed.