The good news is its a good simulator. Just like to 3rd edition was. If you want to semi-accuragely portray human combat it works really well. Particularly if you use the companions expanded wound rules.
It would help if you could get a Companion.
Books from the past ten years or so seem very hard to get....FM3085, FMSLDF, ATOW Companion, Wars of Reaving, Op Klondike, the Era reports and more...all very difficult to get hold of.
As for "new stuff".....traditionally, RPG stuff doesn't sell that well for BT. Personally, I'm convinced part of the reason is because there is a lack of focus which contributes to a lack of support. Your Clan warrior PC isn't going to be interested in running a campaign based around the presumption you are an Inner Sphere merc, but a merc company probably isn't going to last long moseying around the Clan homeworlds. There isn't really a strong focus as to the faction or type of characters that are being played and while it is possible to create or adjust campaigns to suit, that's a good bit of work many aren't prepared for.
BTs reputation as rule heavy also doesn't help...and while there is a points based system, it isn't given the same focus as the standard character creation system. More, I've played several MWs games across different editions with many groups, and many of them come across more as BT games that offer a sideline RPG element rather than actual RPG games. The focal point often came down to the BattleTech game with the RPG character.
Maybe my experiences are different, but from what others have said, I don't think they are exactly unusual.
So, we are stuck, I think, with the RPG side being "tacked" on to the various sourcebooks we have rather than full fledged support of the type we get with games like Shadowrun. Which is a pity - the RPG focussed sourcebooks have tended to be amongst the best sourcebooks and best reads in the entire franchise. It's just a pity, in a way, the RPG focuses so much on BattleMechs but(to a degree) that is inevitable given the links with the main game.