Sounds like nobody's found the system frequencies yet...
Possibly Fleetconnect but unknown how good is coverage for that area; and they would likely add temporary frequencies which may not show up in TAFL; similar to what happened with Ottawa Race Weekend (site went from 3 to 5 frequencies).
Not sure if Closecall works reliably on DMR repeater outputs.
Strategies which could be used:
(1) If you know it's UHF, manually scan sub-bands 420-425, 451-455, and 460-465 with small antenna close to site, with attenuator on. Note active DMR channels. Look up in TAFL for additional info if any. (helps to know what active DMR VC's "sound like" on analog).
(2) Could scan input ranges as in (1): 409-410, 426-430, 456-460, 465-470.
(3) Use laptop with SDR, look for very strong signals.
(4) If it's not UHF (antennas should give a clue), may need a lot of searching. For commercial use, generally start with 162-170.
Dave