there is an RB seat lock complete with clip and two keys for 22.00 euro on the e’bay France site that I saw earlier this evening.It does not seem to have the clasp that holds the
seat in position but this could quite easily be made.If you can’t find it,let me know and I will try and get the article number.(e’mail email@example.com)
Dave Silver contact details are https://www.davidsilverspares.co.uk/. There is also a complete OEM RB lock kit (Ignition switch and seat lock) on Ebay 181482135498, its expensive but will mean you only need one key.