You might need to define your requirements a little bit better. We have a 50kph M+F line and at that particular site we didn't have a boiler. We just put in a small electric steam generator.
Perhaps start here: http://www.bryant.com/products/boilers/bw9.shtml
Is there a reason why your current boiler is not up to the job? People do this two different ways - "normally" people install a sterile grade steam filter (stainless steel) in the steam line - the usual suspects like Pall or 3M can help you out there. If you have black steel steam pipes I would go stainless from the outlet of the filter to the keg racker. Otherwise, some breweries will actually go to the extend of installing a pure steam generator - this uses a heat exchanger to generate clean steam from the "dirty" boiler steam. But this is going to a level that is probably beyond what you require......
Anyway, start with the keg line first - determine the kg/hr peak flow you require and go from there. Make sure it is big enough to supply that, otherwise the water level will bounce all over the place and you'll end up with all sorts of alarms (we have a little bit of an issue with that I believe).