there are several products available from these seeds: http://www.thegoodscentscompany.com/odor/cardamom.html
i don't know about an good affordable cardamom oil, check some suppliers and see what they offer i would say. there are several threads about good suppliers in this forum.
cardamom tincture, i don't have a recipe, but i can't be that hard i think. there's very little water in these dried seeds. the unknown factor is the strength: how many seeds with how much ethanol. have you done a tincture before?