123.45 is assigned to station(s) in France and hence must NOT be used in this country due to interference problems; if you really must request a frequency to use ask DAP first.
Military used to have 243.8 for a practice frequency (may have changed) so how about something else starting 121.xxx for the practice one?
There are several frequencies assigned to research agencies fror 'trials' use which are rarely used eg 118.75; 126.4, so frequencies must be available; there are also several frequencies in the 'air' band assigned to VHF TV transmissions, but these may be on different modulations.