I just checked on Ebay and Bugpiper is offering real MOD kilts in Royal Stuart and Gordon in all sizes. I would guess that he could get any other MOD tartan (Black Watch etc).

Military men aren't all small and slender! I bought an MOD No2 dress jacket with a 48" chest and 42" waist on Ebay a while back.

Here's the onetime Pipe Major of the Black Watch, a huge man: