You can google for an online purchase, but shipping costs would bite. You can find 5/8" x500' at Lowes for $54, if you have them or HD close. Or a landscaping supply.
Looked at the compressors you cited. They may say the 60C is only good up to 1 acre, but I suggest you do the turnover calc for yourself. For my ~1 ac pond, 2-3 CFM is more than enough. Think you don't need the 4CFM of the 1/2 hp. Vertex supplies the lift rates for their diffuser, dunno if your source provides that info, but you could call and ask them if not on their web site.
