There were dozens of different top break models made by Harrington & Richardson. Your best bet will be a search engine, such as Google. Select IMAGES, then Harrington & Richardson. The link below takes you to ONE such image- a nickel plated, top break 38 S&W hammerless revolver by H&R.
What years did they make the 38 top break revolver? How can you know how old one is?
A top break revolver
50-150 USD or so
Cornell Publications
What is the value of iver johnson 6 shot top break revolver?
If you google it, yes.
Midway USA's Gun Stories - 2011 Top Break Revolver 1-6 was released on: USA: 20 June 2011
Impossible to answer without a serial number.
$ 150
25-100 USD
Seldom exceed 100 USD
Yes, in several variations.