In Odoo, Product is what is linked with the website and hence we get to decide if a certain product can be sold or not on the website, However, when a product is published all of its variants are also automatically available on the website.
The following is a workaround which allows you to see all the variants but not allow visitors to purchase some variants online.

Product Variants are created by adding Attributes and Values to a product. There are 2 ways this can be achieved.

1.     Using Pricelists

2.     Changing the Default Extra Price

Updating Pricelist

This method can be used for any case, irrespective of the number of Attributes a product might have.

Create a Base Product

Create all Attributes and Values Needed and Add them to the product. When creating the Values, do not add any Default extra Prices.

Go to Website -> Configuration -> Settings and enable Prevent sale of zero priced products under the “Shop – Products” section.

Set the redirect button to a URL you wish for them to be redirected to, this can be a page with a form that creates a lead for the specified variant, or it can be a page with information as to how to reach out to the company to buy this specific variant.

Enable Pricelist from Sales -> Configuration -> Settings.

Go to Sales -> Product -> Pricelists

Create a New pricelist called website pricelist.

Add all the Product Variants which will not available on the website and set their prices to 0.

Set the Pricelist on the website from the Pricelist configuration.

When the Variants in the pricelist with 0 price are selected on the website they will not be available for sale.

Changing the Default Extra Price.

This method only works if the product has a single attribute with several values.

Create the Base product with 0 Sales Price.

Create the Attribute and add the required values.

Add the total sales price of the whole variant to the Default Extra Price section.

Set the Default extra price on the variant value you wisht to not sell on website to 0

Add the Attribute and Values to the product.

Enable the Prevent Sale of 0 priced products checkbox on the website Settings.

When the variant is selected on the website it will not be available for sale.