There is no website with which I am familiar that has the information you need. The following reference books are the best way to obtain this information:
Worldwide Guide to Equivalent Irons and Steels, 4th Edition
Regarding 13CrMo4 4V, I do not know if there is a direct US equivalent or not. This grade appears in DIN EN 10273, which is similar to ASTM A 739. Grade B11 is a similar Cr-Mo steel, but is not specified to be alloyed with V. I do not know if the mechanical properties are specified to be the same as the EN standard. I would investigate this alloy further an alloy steel bar supplier.