There were two Colin, one standard one and a high sided one often known as a bread carts for some reason. You can get the smaller one as a resin kit from golden arrow models and it is suitable for use behind V1's etc however for the U2's you need to scratchbuild it. The reason why some U2's had the old tender was because they were from the U, and U1's when being converted.
On another note, if you want to model a U2 (or mogul) with a Stanier tender, you cannot use any that are RTR this is because the length is longer than it should be, to fix this you can either cut down the length of the tender or by a brass kit from brass masters.