The little Zebras are Indian HMT tractors that were imported and branded along with Zetor in the U.S. in the 90's. You can search HMT on the web and find their home site but they have no U.S./N.A. site or network.
Plain, basic little tractors and as advised above your best bet for parts/service is a current Zetor dealer.
I know that Bill's Tractor of San Antonio... .
PARTS FOR MAHINDRA TRACTOR, BRANSON, ZETOR, STIHL & ATV'S - BILLS TRACTOR an online bank of available parts for Zebras and they indicate when a part is subsituted.
That being said, a lot of things you likely need can come right off the shelf at the local NAPA, Chief, or whatever you've got. If it's a good straight little tractor and the investment is minor I would not let that shy me away from it.