super 5 wiper blades

seems I have tripped up at the first hurdle of my retro ride ownership. Just spent 10% of the cost of the car on wiper blades I have been assured will fit but dont.

can anyone help me out? its a 89 renault 5TR, and the arms are not the hook type, The new blades (18") simply slide on to the flat arm. I did get some universal ones which came with a slide on clip (as well as a "hook" adaptor) but the width of the arm is too wide to fit.
Anyone know where I can get some or will i have to resort to grinding and filing the old arms to suit?

buy a couple of clio arms from a breaker they must be a similar size, then you're bang up to date and will be able to get cheep blades forever then

See , it's all very well being able to afford a classic but the running costs need to be taken into account as well