I have the same saw that I recently fixed up. It’s an impressive saw for its class so I put some money into mine. eBay is usually the answer for 4600 parts. There was NOS air filters the last time I checked, but they aren’t cheap. Sawagain.com also has some 4600 parts, but not a huge selection.
I don’t know why, but Echo used many of the exact same parts on different saw models of that era but changed the part numbers from the 4600 model numbering. Some of the odder parts you need might be found searching the similar models of the era, such as the CS-4400, CS-4500, CS-5000, etc. I’m guessing the oil pickup tube you need could be found that way.
That being said, 4600 parts are drying up and I still need a couple of things for mine to replace things that are wearing out, but that I can’t find on eBay. I’m still searching for a parts saw to keep mine going longer. I’d suggest watching your local Craigslist or Facebook Marketplace for a parts saw for your 4600 if you like it enough.