Mongo has a list of available commercial service providers . Most of them are a "private server". You are unlikely to find anything outside of private servers that will allow you to install Mongo on your system.
This is too new, it doesn't look like MySQL or SQL Server, where many vendors have just created separate farms for these things.
, - "Maximum ASP.NET", Mongo "-", MongoHQ. .
, , VPS, , , :)