You can set your products as pre-orders in Simple Store to collect payments for products that currently can't be shipped. This is a global setting that will apply to all (or none) of your products - not a setting for individual products.
To active the pre-order option for your product, go to the store > [SHIPPING] > Pre-order option. Check off the “Show my product(s) as pre-order and set an estimated delivery date.” option, then set an estimated delivery date below.
Click on “Update” button on the bottom of Shipping panel to save your changes.
Then publish your site, the [BUY NOW] button will be changed to “Pre-order” for all products after you active Pre-order option. Your set estimated delivery date will also be displayed in your product description.