GLR Kennions in the U.K. have plans and castings available for 2 locomotives that are virtually identical to "Rocket". Both were designed by LBSC back in the 1950's, and many have been built, and they are known to work very well. Both are in 3.5" gauge.
The first one is "Rainhill" by LBSC. which is a very close operating copy of "Rocket". It is different in some aspects, to make it a successful runner, and it is KNOWN for actually pulling a person on a track.
The other version is "Invicta", also by LBSC, also known as a good runner, and also known for pulling people on a track. This is a later version which LBSC developed to simplify building the locomotive.
I have plans for both "Rainhill" and "Invicta" but decided to build "Rainhill" as being closer to the original "Rocket" . The loco is named "Rainhill" as that is where "Rocket" was originally tried out and won the competition in the "Rainhill Trials"
The thing you must remember, and which LBSC often stated, is that "Nature Doesn't Scale" which means that actually building a "Rocket" to absolute scale will give you a locomotive that will not run and cannot carry passengers. This is the reason there are minor differences in these locomotives, to make them actually run on rails, AND pull a driver, as small as they are!
:Reeves2000" of the UK also have plans and castings for the first locomotive ever built, "LOCOMOTION", in 7.5" gauge. This is very near perfect scale, but is a fairly weak locomotive. It is also very complicated, but if you want an early locomotive, this is another good choice. Although there are changes to this locomotive as well, it is a nearly perfect scale replica, even down to the odd wheel castings, etc. that were used on the original. (3 wheels are identical in pattern, and one is an odd and different pattern, But this arrangement has been confirmed as being on the original locomotive, which still exists and is on display.) This model also has extensive woodwork required for the tender used.
If you are committed to rail history, build a "Locomotion". If you want a small locomotive to steam up and drive around, build a "Rainhill".