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.