OK - thanx for checking on that. I'd found some AC designs on the net that required that part, and it seems that was the only hidden part I couldn't find - didn't even know it existed until I saw those designs that used it. Just knowing where it can be found in the game would be nice, and besides, it nags me to think I missed something in there!
Anywayz, here's one of the designs I found that caused this fuss:

Head: HD-H10
Core: XXL-DO
Arms: AN-25
Legs: LN- 1001-PX-0
Generator: GBX-XL
FCS: TRYX-QUAD
Boosters: B-VR-33 or B-PT000
L. Arm: LS-3303
R. Arm: WG-RFM118
R. Back: WM-MVG802 or WM-X201
L Back: WM-PS-2

M.K.