The remington tyrant is just a chineese b19 with a thingy (not sure what else to call it) on the barrel I have the same axact gun qith a standard barrel and mine's called a firepower fp1, anyway you might have better luck on the Chinese airgun gate just call it a sunthetic stock b19 variant. . Also for a sling you could try a shotgun/ muzzleloader style that just loops around the barrel and stock, or tye on parachord loops.
Any idea if the GRT-III is the best trigger upgrade, or is there something better?