When I cannot get the Kolsch yeast, I often utilize a primary fermentation using the US-05 Ale yeast and then a two-week lagering period. While this fermentation schedule is not typical of Kölsch-style brewers, it is also not unheard of, as many of them utilize this schedule. Please note the use of US-05 is not a traditional yeast strain, but is a decent substitute. If you want a more authentic yeast, go for Wyeast 2565 or White Labs’ WLP 029.
I typically go ahead and keg the beer after primary, and then store in my serving fridge for a few weeks until it is ready to be served.