Below is an Ebay listing I found earlier in 2013, but am unable to find any more about them:
Bamby cars one wheel trailor: fits Peel Bambi Berkeley Isetta Messerschmitt micro. Hi folks, now for something different, bamby designed single wheel trailor, the two pictured are NOT FOR SALE i will make to order, the first one was designed to fit the peel p50 and it leans in on corners, great safety feature, it will fit a bamby also, with a little extra work i am sure i can adapt the hitch to fit most microcars and probably most motor scooters, it is retro styled and colour is in the gell coat, it is fully wired, indicators, stop and brake, and has a spring loaded centre stand easily operated with one foot, the lid lifts off for storing your shopping, camping gear, tools, spares etc, the tyre is e marked, speed and load rated, there is a colour choice and chrome trim is optional, the frame is powder coated for durability and of course the body is grp so rustproof, i have pitched the price at i think a reasonable £650.00 with perhaps part exchange allowance on micro car parts/models or what have you, try me, worth the ask !!! all enquirys measage me through ebay, or phone me on 07856213439 you can get me most evenings on 01673818515, thanks for viewing and hope to speak to you soon, cheers, Alan.