Barabarians have weapon resistance later of 20%. If he get a hold of 2 flails of East Haven dual wielding brings him to 60%. Are there any other ways to increses this in BG II or TOB? Obviously any additional help could make the Barbarian near invincible against weapons

Jan's armor does, but it's only wearable by him. Orc Leather and the Belt of Inertial Barrier help against missile attacks, but do nothing for melee. There's one item of which I can think in ToB that helps against blunt weapon damage, but since this topic hasn't been moved yet I'm not going to mention it. ;)

Gromnir Il-Khan's helmet...

When bladeslinger chain is joined with a protection from normal weapons scroll. It becomes immune to all normal weapons.

Paladins, Cleric/Fighters, and Cleric/Rangers:

Armor of Faith @ lvl 20 = 25% +
Hardiness (40) = 65% +
Defender(20) = 85%

Barbarian:

20% permanent rather than armor of faith = 80% total.

If you use the David Gaider mod that gives you damage resistances for taking the evil path in Test 4 then a Fighter/Cleric who is evil could end up with 110% resitstance to all physical damage.

A fighter/thief could use hardiness + defender + Jan's Armor with the UAI ability.

That's about all of the total physical resistance ideas I can come up with off the top of my head. I think that they would work but it has been a while so don't hold me to it.

110% resistance with Gaider's mod with an evil Fighter/Cleric is pretty stout.