Critical value for lare number of treatments

I am trying to perform a Post-ANOVA Tukey test to determine the differences between treatments. I have over 50 treatments (k>50) for some of my tests.

I have calculated my Q value, however when coming to determine the critical value and therefore whether to accept or reject my null hypothesis, the tables that I have only show critical Q values for a maximum of 20 treatments (k).

Does anybody have a table which extends further than k=20? or better still does anybody know the formula to calculate the critical Q value from df and k?

Many thanks