They need to take an awareness course to buy a gun. It can be live instructor based, but no one ever does that. There's video based training as an alternative, which is what everyone does. Most gun shops have a tv and the video sitting around and will let you watch it for free and an employee there is a MSP licensed "instructor". You sit down, watch the video (it's only about 20 minutes), and then fill out a form that the MSP conveniently keeps a copy of.
Do not make fun of this video. 90% of the content on the video is a state prosecutor telling you what is legal and what is not. When you can defend yourself and when you can't. They define the exact bounds of the "duty to retreat", etc. In my opinion, it is very informative on Maryland law.
Since this "course" is administered by the MSP, it also passes as a non-resident certified training course for states that require training when applying for a CCW permit. I got my non-res FL permit with the official looking paperwork you get from it.
7 day waiting period. However, from my talkings with some gun shop owners it's considered as a "minimum of 7 day waiting period" by the MSP. Sometimes it takes longer and the gun store may tell you to come back in 10 days just to be safe.
I got my handgun at Bart's Sports World in Glen Burnie. But that's because I know the guys there and have shot with them for the past 5 years. They have a decent selection of handguns and rifles, but they charge MSRP for them. That'd be pushing your "hour within Frederick" requirement too. It shouldn't be hard finding a dealer out there, though. All the other shops I frequent are on the Eastern Shore and way out of your travel range.