Increase limit of dropdown

Hi,

I am creating custom fields that will be part of customers data. The fields are:

  1. Company Name
  2. Project Name
  3. Saleable Unit

For field number 1 and 2, they are related. The Project Name will show only if its related to the Company Name. For example, it will show the only list of new project, if we choose Company Name -> xyz.

I want all the saleable(saleable unit) block which are unsold should come in a dropdown.
I have tried but it’s only showing 20 elements I want all the block which are unsold for that particular company and project