You are able to limit the number of passes available on a "per-day" basis. In other words, you can set a maximum number of passes available per day. Set this on the Options screen via the Registration tab. 

Limiting the overall number of passes

If you want to limit the maximum number of available passes overall, there are two ways to do this. 

By using Pricing Groups (i.e. no public passes) you are able to set the total number of available passes by limiting the cumulative amount of all passes. Create a registration/promo code for each of the Pricing Groups and then set a capacity. Make sure that the capacities of all Pricing Groups add up to the total amount of available passes.

Another option is to have the daily maximum on the Registration Options screen equal the total amount of passes that are available. Each day, reduce the daily amount by the amount of passes that were sold the previous day.