Bit

I think you need to tell us a little more about the work your trying to perform and to which code you must conform.

ASME Section IX does not recognize pre qualified WPS... They must all be qualified by testing with the exception of a few instances of SWPS (Standard Welding Procedure Specifications)

There is no such thing of a prequalified  PQR... at least not to my knowledge.

We may also be struggling a bit with language.  So do tell us a bit more about your project.

Materials, process. code compliance... everything

P numbers don't apply to DIN nor JIS steels.
You can have a rough idea as to which P number a given DIN or JIS steel corresponds comparing its chemical composition to the chemical composition of P numbers steels. To facilitate your job, I can tell you that there are some approximate steel equivalence tables around.
Attention though ! This will give you just a rough idea, not an exact equivalence.
Giovanni S. Crisi
Sao Paulo - Brazil     

You may find the information you're seeking in ISO TR20173-2005.  This is a Technical Report which has compiled the steels of several countries and where feasible, has applied an ASME P Number or S Number.
I agree with Lawrence as to the pre-qualified vs SWPS.

We use the UNS number.  If you have the DIN or JIS number, AND it crosses over to a UNS number, you can use that to match it to any ASME material that has the same UNS number.

It's a mouthful, but it has worked for us in the past.  We use three books pretty religously for this type of search:

CASTI Red Book (non-ferrous metals)
Casti Black Book (ferrous metal)
UNS Number Cross Reference

The first two have cross reference charts for many materials that have both Euro and Asian identification (and also have a UNS).  From there, many times the actual ASME cross reference is available; but if not; use the UNS cross reference guide and it will list all applicable specifications.

If you have a specific, post it and I'll give it a shot.

Charles.