What signs of damage have you seen on your tree? Silver lindens can be susceptible to damage from a number of pests including aphids, scales, mites, and others. Silver linden has been reported as showing some resistance to Japanese beetles because of the hairs (knows as pubescence) on the underside of the leaves, but that doesn't mean its immune.
Long story short, there may be different treatments depending on the pests you are dealing with.
While I cannot make a specific recommendation, I would definitely check out
this database of arborists
from the International Society of Arboriculture (ISA) as a start. You can search by zip code and distance.
No signs yet this year as its leaves are just budding out now. I'm want to spray this year in the hopes of preventing a repeat from last year where the tree was badly damaged.
I can tell you it was Japanese beetles for sure because last year the tree was completely covered in them in late June / early July and the leaves were badly skeletonized thereafter. They very much enjoy eating Linden as I can testify.