Wojo, believe most King Souper's grocery stores have them, including one along I70 near Golden. A lot of ski shops such as a big one in Idaho Springs also along I70 has them. Where are you going to ski? Main thing is don't wait until you are a couple miles from a given ski area, the local places are not likely to have discount tickets for adjacent mtn. Some of the resorts offer multiday or internet offers on their websites which can also provide a price break over window price. Suggest you go to www.epicski.com
and search for - colorado discounts, should be some specific and recent info there. If search fails, ask question on their board.
Have fun and give us some feedback when you return.
PS: you might also google denver area king soupers and safeway grocerys to see if their websites describe ticket offers and convenient store locations.
PPS: if you think you will get out there more than once in the season, some of the season pass deals pay for themselves in about 10 days.