Edit: The longest section of Gemora between Mishayos in the Bomberg edition of Shas is from the first Mishna in Chelek 90a till second Mishna Chelek 107b (about 17.5 daf)
The first mishna in Sanhedrin 2a- 2b till the next Mishna in the second chapter 18a is the second longest gap (16.5 daf).
Pesachim 99b- 114b (14.5 daf)
Bava Basra 42b- 56a (14 daf)
Rosh Hashona 2a- 15b (13.5 daf)
Kiddushin 2a- 14b (12.5 daf)
Chulin 42a- 54a (12.5 daf)
Yoma 2a- 14a (<12.5 daf)
Shavuos 2b- 14a (11.5 daf)
Chullin 2a- 13a (<11.5 daf)
Yevamos 2a-13a (11 daf)
Brochos 54a- 64a (>10 daf)
Menachos 28a- 38a (>10 daf)
Note: I've only included Gemoros with over 10 Daf of Gemora between Mishnayos Thanks DonielF for input.