From what I saw of a Winnipeg Blue Bombers game two years ago, the event staff were using Motorola MTS-2000 radios, which looked to have gain antennas on them. Judging from the looks, they may be on a UHF, 800, or maybe even a 900 MHz trunking system. Have you searched through those areas when there is a game in progress? However, I would suspect that since the system is probably designed to cover the area around the stadium, it's more than likely a low-power system. Therefore, you would have to be in the nearby area.
73's
Ron