While you will not find a hybrid "Ethiopian Reina Valera," you can find Spanish translations of the Ethiopian Bible, though they differ significantly in style and translation philosophy from the RV.
If you just want a free Reina Valera PDF (Protestant canon, 66 books), that’s legal and widely available (e.g., from BibleGateway, Sociedades Bíblicas Unidas). But that is the Ethiopian Orthodox Bible.
for the Old Testament (based on the Septuagint) alongside a traditional text like the Reina Valera for the New Testament 3. Critical Review of "Free" PDF Links Spanish Orthodox Bible Options for Study