The OEM oil filter for the Kymco Yager GT 200i is apparently Part# 1541A-KKC3-900 Model# SH30DB $19.00
There is an alternative, from Britain I believe, that KymcoForum member CROSSBOLT found. It's called the HiFlo Filtro HF562. It's an exact replacement for the OEM filter, except it's got more pleats (and hence more surface area, and hence more flow).
Now, if you do a Google search on that filter, you'll get a whole heap of websites overseas that are selling it, and if you do an advanced search to filter those out, for some reason you won't get many results of American companies selling this filter.
But, I found one:
DennisKirk.com
Part #: 304961
$3.90
I just ordered 10 of them. Shipping was around $8.00 for the cheapest shipping option, but they've got plenty of other shipping options if you need the filters fast.