As shown on here; https://sellercentral.amazon.co.uk/help/hub/reference/GHGHDMU4X5K9QGCV#mnd_2jc_jcb__section_v4q_4lf_ghb

4. Future Launch Date

A common reason for an ASIN being unsearchable is because it has a future launch date. In other words, it is not yet possible to buy the product. 

To be searchable, an ASIN's launch date/offering release date must be in the past.

Note: 

Check: Check if your ASIN has a future launch date by reviewing the Offering Release Date.

Diagnosis: ASINs with future launch dates are not searchable.

Fix: To make it searchable now, update your ASIN's Offering Release Date to a date in the past.

Also I would check that you have added inventory on the listing and saved.