northernbrewer.com. morebeer.com, and midwestsupplies.com are the three I tend to order from. If you just need hops freshops.com or hopsdirect.com are great as well.
For pH are you talking about your water pH? It is the mash pH that really matters. Some gypsum will lower the mash pH and adds sulfate which helps the hoppy bitterness come across as crisper. If you want to lower the sparge pH some lactic or phosphoric acid would be a good choice.