I use a mix of B&W, Heliopan and several Hoya. All work fine, are well made and will last for ever with normal care. ( I believe that Hoya made own-brand filters, and even some lenses for some of the Japanese camera makers? ). I've no experience of Lee, though I believe they are more expensive and perhaps aimed more towards professionals and movie makers ?
I have bought many filters though Ebay with no problems, despite its reputation....just search for what you need....e,g, "B&W 49mm orange", or "Hoya 52mm" and you should get lots of listings. Check that the seller has a good Feedback rating, read the description carefully for any faults, and whether the item is new or used, and I'm sure you'll be fine.
TBH, I don't find a
huge difference between "light, medium and dark" filters in practical use....I'd suggest trying a medium yellow or yellow-green as a start for landscape use.....maybe don't worry yourself with dozens of different sorts until you've thoroughly tested just one or two.