By asking everyone in my tree - even the ones I didn't know very well.
A key to asking your relatives is to make sure they know you are not trying to claim the family heirloom. Assure them you are simply wanting to admire the items they have from a common relative. And if they could take pictures for you, that would be great. Better still, depending on where they are located, if you can meet with them to take the pictures, that would help more!
Another important question to ask family is if they have any pictures hanging up on their walls. Another true story - I asked a few times if my relative had any pictures and they said no... until one day they realized they were hanging on the wall. Those items we pass by every day might not stick out as family heirlooms.
Another personal true story from my genealogical research. A phone call led to a get together at a relatives house. It turned out they had discovered a cache of family pictures and document in their attic. The list was extensive: chattel mortgages, notes, canceled checks, hundred of post cards, and hundreds of pictures. The vast amount of information contained in the "collection" was immense and most over 100 years old. After 12 months of organizing and cataloging the information, several discovers were made. Contained in this set were people to attach to family names (never before seen) as well as new names to go with new relatives (never before recorded), and personal written post cards detailing the everyday events over several years. If we didn't ask, we wouldn't have discovered this and it might still be in that attic to this day.
So if you have not asked your family where you might find family heirlooms, pictures, documents, and more, then don't wait another day. Start asking today! Keep a record of who has what and be sure to ask them if you can take pictures (or if they would mind).
Keep looking! Those items are out there. You too can find great family treasuries that you never knew existed and your family and all the descendants will certainly appreciate it!
Your cousin with lots of pictures...