In the GPR I have I use Tom Fuller 3/4" black english frints from
www.OctoberCountry.com You will find them good people to deal with.
As far as the barrel goes, this is the first time I have heard anyone complain of the barrel being too long.... That is one of the unique features that make is "sorta" resemble a real Hawken..... You could have the barrel shortened or buy a replacement barrel for it. Sounds like possibly the GPH would have been a better rifle for you with the shorter barrel ?
However, I am not one for upgrading mass produced low priced ML'ers like buying dif. barrels, locks, triggers, stocks, etc... I shoot them as they come & learn to make work what they came with.. .. IMHO, I feel it is usually not necessary for these upgrades & usually one is putting $ 200-500 more in a rifle that is still a $300. rifle... However, others have different opinions of these upgrades & one must choose their own path....
If it were me & I didn't like it as it is, I would sell it & buy another rifle but go someplace & shoulder one Before purchasing it, so you don't have a repeat situation.