You can try reaching out to Shopify Expert Developers or independent freelancers on platforms like Upwork or Freelancer. You can post a project description stating your requirement for adding a local payment feature for IDeal on your website and receive proposals from interested developers. You can then review their portfolios and ratings, communicate with them to see if they are a good fit for your project, and ultimately select one to work with. You should also clearly communicate your budget and timeline for the project to ensure that you find a developer who can deliver within your constraints.
In my opinion, developing this feature is not a trivial thing at all. If you are not a technically aware person yourself, make sure to find a proficient Shopify development company which can develop this functionality successfully.
Co-founder at Whidegroup, e-commerce development company from Ukraine - 10+ years of experience with SMBs - Deep expertise in custom development & optimization E-mail: email@example.com