I don't know if it can help, but for modern French vehicles of that type, one can search in:

1. Goupil
2. Eurovoirie (fr)
3. Cmar (fr)
4. Mega (the same make made the Mega Track (fr) from 1992 to 2000 )
5. Ligier's micro-cars can be used some times

For non-French makes, I think "experts" already know these ones:

1. Bucher Schörling
2. Hako
3. Schmidt (A visual search (fr) can also be done for vehicles sold in France)
4. Johnston
5. Boschung
6. And without doubt much more...

For used ones, IMCDb "knows" already that some makes changed, and I didn't find anything for the others. They seem to have disappear more quickly than the R4

But one think is sure, and I know it will absolutely not help :
The bikes used by Parisian street cleaners for cleaning dogs "souvenirs" were all nicknamed "Motocrottes"⁽¹⁾ (turd-bikes), whatever the accurate brand and model the bike was
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(1) Because it is more or less phonetically close to "Motocross", I assume...


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