Maybe obvious, but people sell them as take-offs on ebay for like 10-15, maybe put up an advert also in the wanted tools forum. the only issue is shipping is gonna be $7, so on top of even a modest price will be like 7+7 to 10eacb=~14-17 shipped min, so if you can get them from SO with free shipping, you're probably better off. most snap on cases and tool rolls are sub 20 dollars, shipped directly. not messing around with ebay and wasting time might be worth the extra 1-2 bucks...if you need a bunch maybe look for a lot-sale on ebay.
edit: hmm YMMV just searched the website and nothing came up...
MAGNETICTRAY
Item: PAKTY219
This Product is no longer available.
eit 2: 224SFFSM is a two set kit, so the OP post may be semi-flat molded plastic tray/holder, not the mag-tray that normal sets come in.