Portals that collect Plant Genetic Resources information from different sources are a good stating point for a search for material.
EURISCO is regularly updated and contains the data of European collections. It also contains phenotypic data for lettuce on a large variety of traits (100.000 data points in May 2017). EURISCO does not provide contact information for seed requests. Germplasm availability is not a criterion for uptake in this database.
Genesys is a global portal to information about Plant Genetic Resources. It contains 3.6 million accessions. The European PGR-data are regularly imported from EURISCO.
International Lactuca database (ILDB)
The ILDB is not limited to European collections. It contains phenotypic data of the project 'Leafy vegetables germplasm, stimulating use', while it also provides contact details of the collection holders. Although ILDB accessions are supposed to be available upon request, this cannot be guaranteed as this depends on the reliability of the provided information. The ILDB is not updated anymore. The last update was in 2010.