Weedeater Featherlite FX26S "Xtreme" 25cc -- new string head?

Someone gift this thing to me. Runs like a top. But it has an aftermarket line-feeder-head thingee (I don't know what it's properly called) that's jammed up good and won't open up, and the guy at Ace said he had nothing to replace it. It does come off the shaft bolt easily enough.
 
For what I'd like to use it for, a light-duty brush-cutter head might be better. Or a head where I can supply my own heavy-duty line like I use in the walk-behind brush mower. (Cuz the pasture grass rips up regular grade line faster than you can blink.)
 
Anyway... suggestions on what might work, and not immediately fall apart? (Lordy, the reviews on Amazon for this stuff...)
 
Thanks!

What I need to cut is mostly cheat grass and sometimes pasture grass growing in inconvenient places (where it's tough to get in with the walk-behind). So it's not going to overwhelm the engine. But I've found that does break up regular line pretty quick, so something heavier would be better, or I'd spend all my time re-feeding line.
 
But finding anything at ALL would be a start. If nothing is out there that works, I'll drill holes in the old head and concoct something.