I spent an hour or two looking online for exactly the same thing yesterday and had no luck. Digital Lawrence catalogs exist but they're available only as pay-to-download purchases:
Antique Books and Catalogs in Downloadable PDF Format
Until someone uploads and hosts free versions, that's about all there is out there right now. However, if you're researching a specific holster and want to know what the code on the back refers to fit-wise, you can always post the fit code here and someone may look it up in a print catalog and let you know what you have. Good luck.