I've had some different experiences getting their website to work. It's a bit confusing and I think they keep changing it. What has worked latest for me is the following:
1) Click the original link:
http://www.kohlerplus.com/model.asp?Mod ... GroupID=64 (if you use Chrome like I do, or some other browser, you can open it in a new tab, then copy that URL and paste it into your address bar in an Internet Explorer Window).
2) I haven't gotten any dialogue boxes the last few times I've done this. You should see the agreement page. Check the "I AGREE" box then select "ENTER AS GUEST"
3) This brings up a list of engine families. Select the "Command PRO(R) Twin CH/CV17-25, CH/CV620-750" Engine
4) Select "CH18" from the list. This should be the top one
5) Navigate through the pages on the next list until you see our spec (CH18-62581). For me this is at the top on page 6. You'll know it because it says "MCELROY" under the OEM column. Select that Specification ID
6) Select whichever parts group you are interested in and enjoy.