CR 4 and CR 6 Beasts for Wildshaping

[NNescio]

As written, there are only one CR 4 and one CR 6 beast in the MM, the elephant and the mammoth.

Are there any other beasts printed in the adventure books?

[Chaosvii7]

Dinosaurs count, and there's a CR 6 one but it's a carbon copy of the mammoth IIRC.

[Zevox]

Dinosaurs count, and there's a CR 6 one but it's a carbon copy of the mammoth IIRC.
I think you're thinking of the Triceratops, but you're slightly off. It's CR 5, and similar to but weaker than a Mammoth.

[Shaofoo]

You could also coordinate with your DM to make up monsters that you could Wildshape into with the appropriate stats as well.

But RAW, it seems that your selection is very limited.

[weaseldust]

Recycling other CR 4-6 creatures as beasts is an easy way to make more that you know fit the CR. E.g. you could easily create a 'beast' that just happens to have all the same stats as a wyvern, except for a different creature type. Obviously you shouldn't convert things like, say, banshees, because they would expand the Druid's options a bit too much. (After all, elementals cost twice as much as equal-CR beasts to wild shape into because of the unusual movement and control abilities they grant.)

[Kryx]

Recycling other CR 4-6 creatures as beasts is an easy way to make more that you know fit the CR. E.g. you could easily create a 'beast' that just happens to have all the same stats as a wyvern, except for a different creature type. Obviously you shouldn't convert things like, say, banshees, because they would expand the Druid's options a bit too much. (After all, elementals cost twice as much as equal-CR beasts to wild shape into because of the unusual movement and control abilities they grant.)
You could also try converting beasts from old editions like PF.

http://marklenser.com/5econverter/ may help.

[MaxWilson]

As written, there are only one CR 4 and one CR 6 beast in the MM, the elephant and the mammoth.

Are there any other beasts printed in the adventure books?

If you're a PC, there's nothing stopping you from trying to e.g. Polymorph someone into a blue whale, or a giant space hamster. You're always reliant on the DM to come up with stats anyway.

You're not limited to what's in the books.