Never heard of buying a fishing license for another states license in the state that your in. So you would have to go to Md and Del to get their license. I've bought non-resident licenses before and always had to buy them from within the state I wanted to fish. Only possible exception would be if they have sales over the internet like Pa does. Here's the web sites. Didn't check to see if they have non-resident licenses, you will have to do that.
https://www2.wildlifelicense.com/md/
https://egov.dnrec.state.de.us/egovpublic/dnrec/disp?doc=publicsubmenu&op=fwlicense