Look for a serial number or sticker. Look in the corners of the glass and/or pull the sashes down and look:

• Side of the sash rails
• Head jamb pocket that the upper sash shuts into

There is no serial number anywhere

Have you checked the other windows? While many suppliers, especially on the new construction end of things, attempt to conceal any information that would help customers obtain warranty coverage, there is usually something...somewhere.

Did you look in the glass for any etchings?

Is this a new build ? I need a bit more info please and some pics of the house would be nice.

I tried to add the photo

Marvin...muntin options

https://www.marvin.com/products/design-options/divided-lites

You will need to call them. How many windows will you need? It's unlikely that they will sell you "product only" for any sort of addition or similar.

Judianna20 are you saying you think they are Marvin?