Agree with the above - we need to replace Gale, and if Trueman is fit and firing he could become that.
As for an NRL prop, there are quite a few off contract:
Martin Taupau - 34, nowhere near the same strike he had in his prime, but has been rumoured to be moving over to the UK at some point
Liam Knight - 29, solid Jai Whitbread type, no superstar
Isaac Liu - 33, but still solid and could bring some good experience to a young pack
Matt Lodge - 29, penalty machine, battering ram, awful bloke
Mahakesi Makatoa - 31, a slightly less effective Isaac Liu
Jordan McLean - 33, huge presence who doesn't run his weight but is still hard to handle, would be a very interesting addition
Sione Fainu - 23 and not very tested, a bit like getting another Atoni or Vagana in
As for Bienek, I played against him a couple of times, and he's a brilliant carrier of the ball but not that dynamic. There's a reason he didn't kick on at Hull, and he's probably playing well at London because he's home again, playing with his mates.