We've found Forcefield TProbe armor inserts from Johnson Leathers work well with our jackets.
Back inserts are the small shape B pad. The Forcefield small Shape B back inserts fit the back armor pockets (16.5"x13.5"), and the elbow and shoulder Limb inserts are Type B. We recommend four shoulder pieces to use in both the arm and shoulder pockets (9"x7").
Both pictured styles of shoulder pieces fit in our jackets. The three jackets we have with armor provisional pockets: