I've experimented a lot with papers and materials lately and wrote down a compact list of things I use on a regular basis. I made this list for my own overview but figured it could be interesting to others as well. I order from companies in Germany, let me know if you want specific links.
Paper
Especially when it comes to paper in etching, there's been one specific problem that apparently many other etchers share: Not being able to print aquatint etchings on commonly available etching paper. With line-etchings there's no such issue. The paper that's usually used for etching is of high quality, 100% cotton, sized internally.
However, across the board of at least 10 different ones I've tested on 3 different presses over the last years, none of the 'good' higher priced etching papers could handle subtle aquatints. The tonal gradients of the prints would turn out flakey and weak, unlike the lines which printed fine. The exact reason for this is still unknown to me, it could be the cotton percentage and its longer fibres compared to the shorter fibre length of the cellulose which is used instead of cotton. The paper I now use for aquatint etchings has a cotton percentage of 25% and is sized inside and out: Fabriano "Watercolour". What's most surprising about this is probably the fact that it is, compared to the fancier etching papers, a cheaper student grade paper. It is age resistent and buffered still and fulfills the standards for ISO 9706. The only disadvantage I found in it is that it's quite hard to tear by hand.
Materials list
These are things that need to get restocked every once in a while. For a complete list of stuff you need for etching, check out this post explaining everything.
Paper
For aquatints:
300 g/sm, cold-pressed, 75 cm x 105 cm, fine. No watermark.
For line-etching:
Arches BFK Rives
300 g/sm, deckled edge, 100% cotton, BFK Rives watermark in one corner (not annoying)
Ink
For aquatints:
Gamblin Portland stiff ink
454g Portland cool black #10 is my fav. Would recommend a darker black for lines, though.
For line-etching:
Charbonnel Carbon Black
For line-etching only! I just use this because I've got leftovers. There could be better ones. Very nice dark lines, though useless for aquatints.
Etching grounds
For lines:
Charbonnel ultraflex
just works
For stopping out and covering up
Any faster drying ground, for example an asphalt based one. Doesn't have to be of high quality, mine is super brittle and old, the company doesn't even exist anymore.
Copper and zinc plates
Try looking for companies that produce copper things for roofs or work in the metal industry. You could get better prices there than at art shops. Polished plates are hard to find, though. In any case make sure they come with at least one side protected by tape/foil.
Acid
Iron(III)-chloride 40% (saturated) industry grade and citric acid powder
Tissue paper for drying and packaging
75 x 100 cm sheets, 18-20 g/sm, acid free, but buffering is not necessary.
Look for shops that sell conservation materials.
Newsprint paper for protection while printing
~20-35g/sm, 50 x 75 cm, usually sold for packing dishes etc for moving house. Try getting recycled ones, but avoid papers that are irregular and cause dents while printing.
Only use this for printing, do not let it touch zinc plates for more than 30min, can damage the plate!
Acid baths/tanks
Acid resistant, higher quality PP, idk if PET is fine too. Often sold as materials for photo developing. Also look for chemistry supply shops.
Spraypaint for aquatints
Most seem fine. Make sure it gets dissolved by acetone and that the lid sprays well. Actually keep that one good lid and put it on the next bottle after finishing one. Good spray lids aren't guaranteed.
Tarlatans
Can only try and find out if it's too stiff or not. I use tarlatans from Boesner on a roll and tear them myself. Pull a new one along an edge back and forth to make the fibres soft.