However, don't let "trade only" stop you from getting what you want.
There's always a way, even if it is only to ask the supplier who they
sell to where you are. Cash is a good business lubricant as well.
Of course if it means that you have to buy a box of a dozen
cartridges, then your interest may wane :-)

If it is that hard to get, buy a box of 10, and sell the spare 9 on eBay!

(With a small mark-up to result in the 10th one being free!)

Sparks....