Another russian finding region for agates formed in lithophysae (“Thundereggs”) is the River Ola :

“...Ola River empties into the Sea of Okhotsk. The origins of the river are located on the Ola plateau. The mouth of the river is located 30 kilometers east of the city of Magadan. River upstream eroding rocks that contain agate. Agate can be found throughout the river and on the see coast near the river's mouth...”

personal report from M. Egorov