Does any modern Buddhist tradition use a Gregorian holiday schedule?

Have any modern Buddhist organization adopted the Gregorian calendar for celebrating Buddhist holidays? Last time I tried to find something simple as Vesak or some of the other common Buddhist Holiday's, they are celebrated on a lunar calendar and differ from country to country, ref: http://en.wikipedia.org/wiki/Vesak#Dates_of_observance I'm not affiliated with any particular organized sangha, so I have two challenges-- deciding which holidays to celebrate, and even after that, there isn't a lot of agreement on how to calculate the day.