Google of "Suvarnabhumi Airport Bangkok ATM machines" produced the following locations which appear to be accessible before IMM. Probably additional ATM's besides TMB before reaching IMM.

TMB banks /ATM cash machines at BKK's passenger terminal:
On Level B near the entrance
On Level 2 near doors 1 & 7 & at Exit C; before Exit C; in the International Hall; and at Concourses C, D, & E
On Level 3 in the passenger terminal and in both Concourses C & E.
On level 4 between doors 1 & 2; at Sections DE, HK/ KL PQ/ RS & W; and on the concourse connector between E & C gates.