Mary, you will find that exit row seats are often reserved for "Elite" level flyers, although they can be assigned at the Gate by the Gate Agents. Bulkhead seats are always saved for handicapped, injured, parents with infants and so on. They can usually be obtained at the gate as well.

Unless you are a Very Frequent Flyer with major status on an airline, you cannot reserve them on line. (although I was able to reserve an exit row on a Delta Connection Flight because that was the only seat left!)

Sorry to be the bearer of Bad News. You can also try to see if your Travel agent can book the Exit or Bulkhead for you.