Agreed, it does work but the effects are anxiolytic/sedating, not very "euphoric" It's made from the borongoru cultivar.
I don't know of any other vendors that sell pre-made drinks online. There is kava candy from Ozia, not sure how that rates on the headiness scale.
If you don't want to bother with the whole preparation process, you could try some Mo'i micronized from Gourmet Hawaiian Kava. Just dump a tablespoon or two in water and drink; no straining needed. Very heady.