party

Invite every trans person you know in your city to a discord with an 18+ chat.

Get them to invite every trans person they know in the city to the discord.

Post an invite link in local college Pride Lounges.

Ask mods in more general LGBT locally-focused discords for permission to post an invite link stating that it is for trans people.

Match with trans people on LGBT+ dating apps and invite them.

March in your city's Pride Parade and hand out business cards with a QR invite code.

Then advertise a party.

In 18 months I've gathered >460 trans people in my discord, over 10% of the trans population of my city!