There have been some converted in the past - check out some of the past projects @
www.dtrsports.com this company imported and specialised in the 124 Spider for many years.
Iirc, you would need a right hand drive steering box and idler box from usually a 124 Sport Coupe, but I've heard there are other options/work-arounds? e.g. afaik, the last of the 124 Spiders (possibly the Pininfarina/DS models?) had a steering rack instead of steering and idler boxes.
(lots of 124 Sport Coupes were scrapped having
donated their st. and idler boxes

).
Some other minor parts are also needed e.g. longer (rhd) clutch and accelerator cables, longer servo vacuum hose etc.
Some small modifications are also needed to the engine bulkhead (firewall) and to the sheetmetal behind the dashboard plus a replacement dashboard would need to be fabricated.