Currently, the "Peer-to-Peer Fundraiser" and "Peer-to-Peer Team "dropdown lists shows a limited number of fundraisers and teams to choose from. They're listed by creation date and there's no way to search or enter the fundraiser or team name that's not on the list.
The workaround is to add the Manual Donation without a fundraiser or team but selecting a Campaign. Then, edit the donation and you should be able to select the fundraiser and team in the right-side panel: