Is there an app for running Go code on an iPad?
As far as I am aware, unfortunately, there are no iOS apps for running Go. You could try to add a shortcut to https://play.golang.org to the homescreen; this effectively emulates the functionality of being able to type and compile Go code. However, needless to say, this requires an Internet connection and so is of limited use if you really need to edit "on-the-go" (no pun intended). 

There are a plethora of developers who have created apps for large varieities of languages, but, as you acknowledge, Go is consistently omitted from their repertoires. If you search for a popular language, like Python, for example, then choose one of the apps for it and look at more by the same developer, there is usually a large range of associated apps, each dealing with its own programming language. In searching for Go apps, I repeated this process many times, and found apps for Lua, Groovy, Haskell and other not-so-mainstream (by which I mean less popular according to TIOBE) languages, but no Go. My search however, was by no means exhaustive, and this seems to be a much better avenue than simply using the built-in "search" feature on the App Store, so, if you are really desperate for offline functionality, I would consider carrying on along these lines (if you have not done so already).

If you can wait to compile your code until you are online (on play.golang.org), then there are several text editors with Go syntax support (Coda for iOS is a personal favourite).