How to get WordPress site to talk to POS?

I have a wordpress site for a florist that needs to talk to a 3rd party Point of Sale system. The POS system has an API. The WordPress site is running on a premium theme, currently using the PayPal shopping cart plugin but would prefer using eShop. How do I find a developer that can make eShop talk to the POS?

Sample XML Order Posting: (What the POS company sent me)

<?xml version=”1.0″ encoding=”utf-8″ ?>
<PostOrder xmlns=”https://POS/”&gt;
<Token>xxx</Token>
<OrderErrorEmail>xxx</OrderErrorEmail>
<Billing>
<CustomerID></CustomerID>
<FullName>first last</FullName>
<FirstName>first</FirstName>
<LastName>last</LastName>
<Address1>xx main st</Address1>
<Address2>xx</Address2>
<Address3>xx</Address3>
<City>los angeles</City>
<State>CA</State>
<Zip>90004</Zip>
<Phone>123-456-7890</Phone>
<PhoneExt>011</PhoneExt>
<Fax>111-222-3333</Fax>
<Email>sir_imtiyaz@hotmail.com</Email>
<Cell>002-563-7890</Cell>
</Billing>
<Shipping>
<Attention>Mr</Attention>
…
.
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