As you may be aware, you're going to face two problems:

First, the CSR-11-R suffix identifies the engine are specific to John Deere and the shaft dia and length, throttle arrangement, and so on.

Second, since you're in California, a reputable dealer won't ship you an engine unless it is CARB certified. Private party is OK, and you personally won't face any jeopardy, but a business won't do it.

For years Small Engine Warehouse in Muncie, IN sold this exact engine both on-line and on Ebay for $199. Apparently ran out of stock last summer. You might contact them, and see if they have a possible substitute.

Tulsa Engine Warehouse also has a large stock of Kawasaki FJ180V, but you'll have to sort through the crankshaft options and deal with CARB certification. Generally their Kaw engines run $300 to $320.

Lastly, you might try to chase a Kaw FJ150V which is a little smaller, but formerly used on JX75 mowers.