I didn't know the liquid vitamins could be used as a soak, duh! If I'd only known sooner...

They have Flukers liquid vitamin and Jurassi-Cal liquid calcium at Hollywood Fish Farm (Cnr of Tawa Drive and Rosedale Road in Albany) and at least the Flukers at Bird Barn (Corner of Lincoln & Pomaria Rds in Henderson). About $25-$29, depending on where you go and which you choose.

[Edit: Forgot PetStop in Mt Eden, who usually have Flukers liquid vitamins, and may or may not have liquid calcium. If you are really stuck for transport, there's always TradeMe, but you'll probably end up buying from either HollywoodFF's or PetStop's TMe accounts anyway, and their TMe prices are a dollar or so dearer than their shop prices, plus postage - but, at least it will be posted to you, rather than you trying to get to them. Postage might work out a similar price to paying for trains/buses anyway...
(If I drove, I'd love to help you out, but I'm stuck out west with only public transport, so I can't even get myself to HFF, and I really need a UVB lamp, too... Why are cars so expensive?!?) ]