Where can we obtain a set of standard mix designs for a given strength? Our testing laboratories are frequently asked for mix designs on such short notice that it does not allow time to calculate them.
You will undoubtedly have to make your own. Any mix design must be checked out with trial mixes and eventually plant batches of the materials to be used. A mix design for one particular combination of aggregate, cement and other ingredients may produce a far different strength when used with another set of materials. Tables from which mix proportions for a given strength can be derived are available in the Bureau of Reclamation
Concrete Manual, in "Recommended Practice for Selecting Proportions for Normal and Heavyweight Concrete (ACI 211.1)" and other sources. However, these are only first approximations. All such proportions require testing, usually followed by adjustment.