Right now there is no bonus to only reduce physical damage from a race. If a server had that they must have solved that by changing the source code. I've never seen a server like that, though.
If you want that too you'd need to learn how to code yourself. Or ask those servers for a diff.
https://raw.githubusercontent.com/rathena/rathena/master/src/map/battle.c
The function you are looking for is:
int battle_calc_cardfix(int attack_type, struct block_list *src, struct block_list *target, int nk, int rh_ele, int lh_ele, int64 damage, int left, int flag){