Honda only sells paper copies, $34.95, and that includes shipping. Pretty cheap compared to taking the engine to a shop for repairs. The one for the GX340 is a full 124 pages. Any digital copies you might find online are pirated, and many not include all the pages/information for your exact engine. If you just need a page or two, I can share a couple online, but if you doing a full overhaul or extensive work, having your own paper copy is truly priceless compared to the frustration of not having one.
With regards to the carburetor, my catalogs still show all versions available. Stamped on the side is a code, "BE80D" for example, I'd need the code off your carb to match it exactly. Full list price for a completely new carburetor is $64.13, but many dealers offer discounts.