There are still a lot of parts around, both online and in people's garages. It's always worth asking on the forum first - a lot of us will have bought the parts you're looking for somewhere, and you'll always get a quick answer.
But you need to be absolutely sure what you're looking for, and for that we need to know the numbers on the underbonnet oval plate (e.g. R1128), and on the engine plate (e.g. 688 D7/12). If you went to a Renault parts department in, say, the 80s, the first thing they'd say was 'Oval plate number?'. That number will enable you to be sure of the part number (for R4s, they usually begin with 7700 or 7701, followed by six numbers). Then if you do a search for that number, you'll get other manufacturers' equivalents - indispensable for eBay, for example, where you can still track a lot of stuff down. It's easy to end up with the wrong part, though (even Renault parts people occasionally made mistakes), but the year of manufacture plus oval/engine plate numbers will virtually eliminate that possibility. As the old saying goes, a few pictures are often better than a lot of words....
If you pm me your email address, I'll send you a parts pdf.
Good luck with the restoration!