Lois Medici, FWIW, our studio's paper supplier/wholesale sale agents tell us that pretty much every paper made these days is alkaline buffered with calcium carbonate. Dr. Mike Ware's alt photography website talks at length about the difficulties of finding non-buffered papers and how the St. Cuthbert's Mill papers were specifically formulated to get around this too common malady with modern papers. Modern papermakers have had to change the chemistry of the paper making process to comply with environmental laws in most countries. From what I've read, it used to be that paper making took place in an acidic environment that made great paper but created environmentally problematic acidic effluent. Today's papermaking process is more environmentally benign but the paper requires alkaline buffering to remain ph neutral over time. I've verified this with Arche's paper mill's representives, they assured me that the Arches Aquarelle is indeed alkaline buffered.
Quiver, if you are going to have success with cyanotype, you're going to have to mail order your supplies it seems. Staples and Walmart aren't going to have any paper suitable for making alt photography processes. Any mail order art supply place will carry Arches papers. Daniel Smith, Utrecht, Dick Blick, Cheap Joes, all of these businesses supply Arches. I've found cold press watercolor paper to work better than hot press if you want an even coating and deep blues. However, for photographs with fine detail, hot press gives better resolution. If you need to order chemicals, I order from artcraftchemicals.com, Bostick & Sullivan, or The Photographer's Formulary. BTW, swabbing vinegar over paper and letting dry isn't going to acidify paper, that's too weak to do any good. Something stronger like Lois Medici suggest is called for. (You can easily get hydrochloric acid in the concentration he mentions, it's sold as "Muriatic Acid" in hardware stores and swimming pool supply stores.) The advice to use non-alkaline water to develop and tap water to rinse is good advice. (In my studio practice, I can't do this practically though, as we tend to work too large to do this. We regularly make cyanotypes up to 51" x 8 feet in length. Thus the need to acidify the paper with oxalic acid.)