Hello!
There is some information about callsigns/frequencies of SITRO-AIS flock from satellites operators:
Name Callsign Frequency
SITRO-AIS-13 SC3231 401,010
SITRO-AIS-14 SC3232 401,035
SITRO-AIS-15 SC3233 401,055
SITRO-AIS-16 SC3234 401,075
SITRO-AIS-17 SC3235 401,095
SITRO-AIS-18 SC3236 401,115
SITRO-AIS-19 SC3237 401,135
SITRO-AIS-20 SC3238 401,155
SITRO-AIS-21 SC3239 401,175
SITRO-AIS-22 SC2310 401,195
SITRO-AIS-23 SC2311 401,215
SITRO-AIS-24 SC2312 401,235
SITRO-AIS-37 SC2325 401,0025
SITRO-AIS-38 SC2326 401,045
SITRO-AIS-39 SC2327 401,065
SITRO-AIS-40 SC2328 401,085
SITRO-AIS-41 SC2329 401,105
SITRO-AIS-42 SC2330 401,125
SITRO-AIS-43 SC2331 401,145
SITRO-AIS-44 SC2332 401,165
SITRO-AIS-45 SC2333 401,185
SITRO-AIS-46 SC2334 401,205
SITRO-AIS-47 SC2360 401,225
SITRO-AIS-48 SC2370 401,245
All of them use USP 2400.