Where can I buy a silver linden in central Bucks County?
While I am not able to give you a specific nursery, I can direct you to the website called Plant Source: Where to Buy Plants in the Greater Delaware Valley Region (link below). This site has a searchable database where you can narrow your search by county and by kind of plant. When I searched it for Bucks County nurseries selling shrubs, trees and vines, I got a return listing of several nurseries, with phone numbers and contact information so that you can call them to find out if they carry Silver Lindens (Tilia tomentosa).Of course you can broaden your search by omitting the county filter and just search on nurseries carrying trees/shrubs/vines in the Delaware Valley.
I also included below a link to our resource guide called Philadelphia Gardening Guide. Use this guide to learn where to buy plants, what to grow, how to connect with other gardeners and where to learn more about gardening in this area. And finally, I included a link to the Arbor Day Foundation's Tree Guide containing a portrait of the Silver Linden. Hope this helps.