I'm from the south of France and I know the downhill close to monaco.
You have the Peille Downhill (Vouilloz and Barel's track, they are both from Peille village) at 25min drive to monaco.
The finish of the downhill is on the Peille road, before the village (about 1 ou 2Kms before). The finisk is on a car parking. The start is close to the RMC radio antenna on the top of the mountain. The access of the start is by road.
You have the San Romolo Downhill too in Italy. 1h of Monaco, the name of the village is San Romolo (a little village behind San Remo). I recommend to you this track. The track is long, technical with rocks on the first section, forest with many switchbacks on the middle and natural bermed on the finish. The finish is at 200m of the village and the start is on the Monte Bignone Hill. The access is by road in 10min for a 6min Downhill.