Well, considering the nature of this whole thing, doing it online is usually the best idea even if you can do possession. It could get strange and awkward in real life but hey, if you're both willing to do it then go for it and deal with the consequences, whether they're good or bad.
And when online, you also got the option of actually mentioning tulpas or not. If your tulpa keeps it a secret then obviously more options open up, but it could be difficult, especially if they want to be honest and share their entire life. Then you are kind of stuck with tulpa communities, where tulpas are understood and accepted.
Tulpa Network is a bit slower way to communicate, but we do have tuppers around here still. You could use off-topic to make a thread for talking (or use the chat thread) if you're willing to wait, maybe try for a penpal somewhere too. IRC is the real time chat option, though the channels can be dead. While it's not an official channel, #tuppers on Rizon is a rather active one most of the time. Depends a bit on the time as most of us there are European and sometimes we all are busy at the same time. It's a tulpa channel for the most part in that everyone there knows about it and probably has their own tulpa or two, but the topics can range from tulpas to everything else. Usually, if you want to change the subject (especially to something tulpa-related), then you just need to talk about it.
You can usually revive dead channels by talking, anyways. Doesn't work always - especially if they're really dead and no one's actually there - but it's worth a try. In my experience it seems that many tulpa channels wait for everyone else to start a conversation, which is weird and awkward. But yeah, #tuppers is usually active unless you're active at strange times and there are plenty of tulpas too. Just, I guess we're usually pretty crude and everything seeing how we have the maturity of 12-year-olds. Any rules can be found
here, if you would like to take a look at them. Not sure if it's for you, but trying to offer you some options and all.