lots of hits, e.g.
http://ja.wikipedia.org/wiki/ハリー・ポッターシリーズの魔法薬一覧

This is in the book I'm reading, and I found numerous examples on the web, such as at:  http://ja.wikipedia.org/wiki/ポーション.

You may also want to cross-reference to the entry for ポーション and/or 水薬.

Alternate versions are 魔法水薬 or 魔法の水薬, but I wasn't sure whether to add new entries for those as well, since their meanings are easier to infer from the component parts (魔法 + 水薬) which are already in the dictionary.