The semas and sema-like demonstrations are popular with foreign visitors, and all seats are often sold out, often in advance. You cannot just go and expect to buy a ticket just before it begins. (If you do decide to chance it, go several hours before it begins.)
The best way to assure that you'll be able to see the dervishes is to reserve your tickets a day or more in advance of what you want to see.
That having been said, I must tell you that it is impossible to keep up to date on the many various dervish groups, the ever-changing venues, dates and times. The information on this page will help you to find a program you can attend, but all of this information is subject to change.
If you have reserved a hotel room for your Istanbul stay, your hotel may be willing to send someone to buy tickets for you. They may charge a fee for this service, as it is an expense for them. A travel agency may also be willing to buy you tickets (for a service fee), especially if you are also reserving other services through them, such as hotels, rental cars or tours.
Silivrikapı Mevlana Cultural Center
The Contemporary Lovers of Mevlânâ Society (Evrensel Mevlânâ Aşıkları Vakfı), a forward-looking Mevlevi group very much in the spirit of Rumi (Mevlânâ), performs the sema each Thursday evening at the Silivrikapı Mevlana Cultural Center, Mevlânakapı Mah., Yeni Tavanlı Çeşme Sok. No: 8, Silivrikapı, Fatih, İstanbul (map; firstname.lastname@example.org, tel +90 (542) 422 1544). The program begins at 19:30 (7:30pm) with a question-and-answer hour, mostly in Turkish, with some translation into English. This is followed by the singing of hymns, then the sema, ending about 23:00 (11pm).
Performances on December 17, are in honor of Şebi- Arus(SHEB-ee ah-ROOSS), Mevlana Jelaleddin Rumi's "wedding night with God" (the night of his earthly death).
—by Tom Brosnahan