I don't think there was ever any implication made that Lupin's or Madam Pomfrey's chocolate was a special "wizard" chocolate - it was therefore likely a regular unenchanted muggle chocolate.

As noted in the comment by gnovice, this question explores the reasons why Muggle chocolate might work: http://scifi.stackexchange.com/questions/9835/is-there-a-scientific-basis-for-the-healing-properties-of-chocolate 

No mention of chocolate in that context in any of JKR sources.