It is hard to find around here. Good luck. I did find it once in an Italian speciality store in Greenbelt. But sometimes the grocery stores are hit and miss around here. I'd think the fancy McKay's in Leonardtown or Giant are your best bets.
I usually use full flavored brand name cream cheese as a substitute.
From my cooking website
Other options are
-Use the "freshest, best-quality" cream cheese you can find
-Mix equal amounts of cream cheese and sour cream
-Mix 1/2 pound of ricotta cheese with 1 cup of heavy cream in a food processor until it forms a homogeneous cream (this substitutes for about 1 pound of mascarpone)