You may look into companies like Trustwave and similar. You can even check all the other companies who they have been using and approach each of these companies. The list can be found on Visa Europe / Asia / USA etc. for AIS/ PCI certified service providers.
Businesses that trade online will need to demonstrate that they are PCI Compliant. Gaining compliance can be a very timely, costly and stressful experience. I would recommend contacting your online payment partner for advice. We are an online payment processor in the UK and we are PCI compliant level 1 (here is our pci compliance certificate). Many of our customers benefit from our compliance by using our payment page for their website transactions (so they do not store card data on their servers, we store it securely on ours). They just need to fill out an SAQ form which significantly reduces their workload but allows them to be compliant to the security standards. We also partner with Trustwave so they too, are a good starting point.