Hi,
When you create custom fields, on the right side of the screen, you have the display options. You need to turn on the backend form display in order to see it on the product edition/creation page.
In the HikaShop products search plugin, you have the possibility to select which fields will be searchable via the joomla search module so you will be able to select these fields.
An alternative is to create a new category tree for your products conditions. Then, for each product, add one of these categories in it (you can have several categories for a product), and then create a new module of the type hikashop content module which will list the conditions categories and upon clicking on one will display a listing of the products with that condition.