I've been going to my local music store to jam with people in the synthesizer section and guitar section. Aside from that, what other places/hacks have you found to jam with people in your area?
It will depend on the city and what resources you have access to.
Connect to Students at a University
If you have a big university with a strong jazz department, they will sometimes sponsor jam sessions where you can meet people. Another way to get connected to the musicians at a university is to sign up for a music class (theory, performance, etc.). You can also take lessons with the university's piano/guitar teacher, which will often lead to relationships with people in the music program. Another option is to attend the concerts and make conversation with the musicians after.
Local Jam Sessions
If you live in a place like New York City, Nashville, Chicago, etc. then there will be plenty of clubs/bars that host jam sessions. You can show up to a jam and meet musicians that way. Even many smaller cities have at least one place that hosts jam sessions.
On sites like meetup.com or craigslist, you might be able to find other musicians looking to jam. Or, if you're trying to reach out to professional musicians, you can convince a local bar, coffee shop, etc. to hire you for a gig. Then you can post on craigslist, etc. that you're looking for a drummer and bassist to hire for a gig.
There's always jam sessions at open mic nights, where attendees are expected to play with others. You may go there as a solo artist, or sit in with a couple of friends with whom you've rehearsed several numbers. At the better open mics, someone will organise who plays with each other, and that can be challenging and fun - playing with folk you've never even met before. When you get better at it, you might even become part of the house band, ready to accompany anyone who turns up. That's the bit I love best.
Otherwise, adverts in music shops, schools, colleges, local rags and social media should find like minded people.
In UK (don't know where you are!) there are sites like 'Join My Band' and 'Bandlist' which provide opportunities for musos to contact each other, to join bands, or just jam.
Check with MEETUP.COM to see if there are any music groups in your area who imbibe in jamming. Also, check out the Musicians Section of Craigslist. Yes, yes, yes, yes, yes. I know, Craigslist is filled with murderers, sex addicts, drug dealers, burglars and muggers. Skype first, ask for a video sample, meet first in a coffee shop. You'll know if you are talking to a real musician or not.
Consider joining a community theater group and play in the orchestra. It is not jamming per se but you will glean valuable disciplinary skills working with other musicians.
Find out if there are any community bands such as orchestras or big bands and inquire about joining.
There are also several software programs that you can jam along with. They are not ideal but may be worth looking into. Music Minus One is the industry standard.
Finally, join a church that plays in the style you are interested in. Many have bands, folk groups, orchestras or small groups where jamming is de rigueur.