You can use the following methodology. The examples below use Eikon Excel worksheet functions. If you're looking to replicate this process programmatically, you can use DEX2 and RSearch Eikon COM APIs libraries.
1. Retrieve issuer OrgidCode from RIC/ISIN/CUSIP/SEDOL
=TR("RU0007661625;VOD.L","TR.OrgidCode")
The above returns 81339 and 13625, which are Orgid codes for Gazprom PAO and Vodafone Group Plc respectively.
2. Then you can use Orgid codes to retrieve the list of ADRs for each company.
=RSearch("EQUITY","RawContextFilter:'AssetState ne \'DC\' and IssuerOrgid eq \'81339\' and RCSAssetCategoryGenealogy eq \'A:31\''")
The above returns GAZPq.L, GAZPqUSD.xbo, OGZDRPEU.MMV, GAZPy.DE etc.