Are they sold anywhere that isn't online?
May want to check your nearby medical supply stores.

What are some experiences of others in regards to the creatine dosage?
Each persons body and baseline creatinine level is different. Therefore, you cannot base your dosage on others dosage.
One thing to keep in mind though, is that there are no upper limits established for creatinine. However, this does not mean you should go overboard with creatine loading. Too much creatine can result in long unwanted bathroom sessions, sitting on the toilet seat.

Also, I am correct in thinking that the lab actually tests for creatinine levels, which are the byproducts of creatine?
Yep thats correct. As muscle tissues are broken down and rebuilt, creatine is metabolized into creatinine. It takes 2-3 days for the body to metabolize creatine into creatinine and be present in urine. Therefore, any creatine-loading should be done at least 3 days before the scheduled U/A.