I think it probably depends on the selling dealer (not the factory). When I bought my 30 amp trailer, it had a starter kit that the dealer threw in that had a 30-15 amp adapter, toilet paper, toilet chemicals, water pressure regulator, fresh water hose, 10 feet sewer hose, disposable gloves, etc.
You might can get your selling dealer to throw a similar kit in the deal, if they don't already.
If not, Wal-Mart sells all the RV common adapters in their RV section in the stores.
2011 Flagstaff 831 RLBSS
I used to be addicted to time travel, but that's all in the past now.