Where can you get liability insurance at a good price for a wedding reception?
There are specialty Lines underwriters that cover this market.
For your Wedding Reception the best place to seek out coverage would be through a Professional Wedding Planner. A Professional Wedding Planner will likely know of Specialty Insurers that may offer this kind of one-off coverage.
Alternatively, you could try your usual family insurance agent. If you already have other long term personal or professional lines coverage placed through your agent and he considers you a valued client he may be willing to find coverage for you.
Since Event Insurance is generally for a rare occurrence, especially for a wedding which is a one off event that most hope will occur only once in a lifetime. Most Insurance Companies and Agents find it too rare a demand in the market place to offer such coverages.