The majority of Spain is unable to comply with overly restrictive UK government legislation. The only size that can be readily sent are those with a trunk diameter of less than 5cm. Occasionally there are batches of palms that are produced specifically for the UK market. For many nurseries this is not feasible nor is not economical due to lack of facilities or shortage of plants in an international market with very high demand.
Before Brexit DEFRA were happy to accept palms in 10l pots and were lenient on the 5cm trunk limitation understanding them to be small plants and so of no danger. Post Brexit the size limits are strictly enforced by Spanish Inspectors (as they should be) and so palms are physically measured before export paperwork is issued. Many palms in 10L pots can be a little over the size limit so they are automatically rejected.
This has resulted in a situation where post Brexit we are unable to send plants in 10L pots which were allowed pre-Brexit under the same set of regulations.
Cordyline australis is still available as an alternative, typically in pot sizes from 12litre to 90Litre with occasional specimens available in 160 and 285 litre pots.
Cycas revoluta palms require CITES paperwork for both export and import now the UK is outside of Europe.