If you are unable to find reliability and validity information on a measure through neither Mental Measurements Yearbook nor APA PsycTests, use APA PsycInfo, which might contain articles, which review the test/measure.
Find article reviews of measures and articles which administered particular measures.
1. Search for the assessment name.
2. Then search for Reliability.
Choose test reliability.
3. Combine the two sets with "And".
4. Repeat for Validity by searching for "test validity" and combining with the assessment.