Are there any resources for learners of Chinese dialects that are close to Mandarin?
There is not much of this available even at bookstores within China. There is even much less for non-background speakers in English.

I personally have been lucky enough to get a book from Peking University Press titled "Practical Suzhou Dialect" which also includes English. I tried searching online however this appears to be a one-off. However, you could try contacting one of the major universities or even going to a university in Henan to see if they have resources available.

There is also this book listed on Amazon Henan dialect of Luoshan but this is not a text book. I have tried seeing if I could find the contents of this online, but only found a site listing an index of what is inside. 

I also suggest asking on Chinese social media sites to see if anyone can help.