Tenders made at the same time as the loco often have a kuid either one more or one less than the loco. The exception to this is when a general type of tender was used instead of one dedicated to that loco. Either way, once you have the right loco and tender combination I suggest you place them on the track and save them as a consist. It makes it a lot easier to find in surveyor. I do this for all steam locos and also for locos where there are several paint schemes for the same loco and tender. It is easy to place the consist and then delete the paint schemes I don't want then to hunt through them in that tiny asset picker window.
I wish more creators would make a consist and upload it as well as the loco and tender. It would be a dream to download the consist and get both.
William