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I'm sure they had a method of numbering them, but I've seen them with numbers from the mid-1000s to the 9900s. Your best hope is to find a picture of one you want to model, and use the number in the picture.
When the site opens, look for 'wheel type' which goes by Whyte notation. Look for 6 coupled, then 4-6-2 or Pacific, and then find the P section for Pennsylvania, etc, until you find the listings of the various purchases of the K Class of steam locomotives.