It'll take some investment but I'd start by finding someone else that needs a code review and offer it to them first. From there you mention that you'd appreciate if they scratch your back as well.
You can probably find some open source projects where you can offer code reviews to other.
Not sure if this is helpful, but I asked family for code reviews for my birthday. (Requires that you know coders.) This might be helpful: https://www.reddit.com/r/codereview/