It's not so bad.
Best I've gotten was smelling some girls' sweaty shoes. We ran track together (prime activity for sweatiness, especially for shoes) and they'd taken their shoes off to do some exercises. When they were a ways away I took the opportunity to sniff them. Fueled my boner for quite some time.
Other than scenarios like that, you'll have to make do with just coincidental encounters. Could get a gym membership and subtly smell the air around girls.Or in public places, hope that one farts around you. Usually Mexican places are better for this because of the beans and all.
Worst case scenario, pay a prostitute, but that gets pricey when you do it often. I was able to get a bit of a discount since there was no touching involved and she thought it was kinda cute.