Potomac MD shiva
If it doesn't need to be kosher, there are numerous options. There is Attman's Deli (NYish) in Potomac. They may even know what a shiva plate is:
A bit more distant but probably best in terms of quality is Wegman's, about 20 minutes away: (240) 499-0700
There is also a Balducci's not too far away and I know from experience that they do a nice platter: (301) 564-3100
I have no idea whether they deliver, but you might contact Brooklyn Deli. they are in Potomac and are quite good.
You might also contact Ize's Deli and Bagelry. They do deliver.