Originally it was issued by Centuri. When Estes bought Centuri they released it aroun 1992 I think.
It is now discontinued and they sell for around $200 to collectors, not builders...but!
If you have the capsule or the plastic part set from the Estes Saturn V you could clone one.
JimZ makes a resin reproduction of the scalloped lower shroud....good luck with that.
The decals are also available fom him or Tango Papa.
The one detail you need is the special tubes!
The "command Module tube is the BT-154 (I think) and it is still available from Estes.
The tank tubes are special too!
Totally Tubular has them listed as the T-.7 body tube.
I'm building one...eventually. Mine is about 50% completed then I got sidetracked.
https://166.82.74.22/showthread.php?s=&threadid=1833&highlight=saturn+1B
I MAY...not sure...I May reissue my 1/135th scale Saturn 1B if I can get more decals sets made.
https://166.82.74.22/showthread.php?s=&threadid=3133
sandman