Getting a coder to perform triangulation
Your reviewers are right! Having multiple coders is a best practice for this type of work. You could try to recruit:

Other PhD students (trades are best - I will code for you if you code for me). 

Masters students in your same lab (may offer trade, co-authorship if they want to help with paper more generally, or payment)

Masters students you have taught (usually would offer payment)

Advanced undergrads who you train extensively (would likely offer payment)

To find these people, you could try to send an email on your department listserv. Additionally, many professional societies have listservs and you might be able to find other PhD students that way. You could also use social media to tap your network.