For tubes and flaps.... I have always gone to GCR tire center...they do big rigs and trucks ....
you may have one near ya:
http://www.gcrtires.com/locations.php
any truck/semi truck tire shop would have them ....as well as the flaps
i got one from tractor supply once...however it was a smaller size 650 in stead of 750....but it workout fine
somebody told me that the goodyear by me also has them...but...never checked...i dont want to hear the song and dance about how the split rims are bad from them....so i goto GCR....and all they get in is split rims
The tubes need be be offcenter stems.... they should be offcenter already if you get:
700750r16lt tube with a tr150 valve stem
the tr150 is the flexable valve stem....not the brass...i prefer the flex stem
i believe the 700750r16lt w/tr150 cross ref with firestone tube pn# 552962
I have been running the 255/85r16 on mine for years and love em... 33" tall and about 10" wide.... Manufacturers vary slightly on the overall size
I used to run bfg mt's this size
I used to run Toyo M-55's
Now I am running Cooper discover S/T this size