I came across a few webpages that relate to your search:
https://bitpay.com/bitcoin-payment-gateway-api
"BIPS.gif BIPS Bitcoin Internet Payment System, Merchant solutions and eWallet for Bitcoin
Bitcoin PayFlow automates the process for accepting bitcoins
BitcoinNotify merchants solution for accepting Bitcoins and updating BTC prices
BitPay Merchant solutions for Bitcoin
BitMerch Bitcoin payment processor with 0.5% transaction fee.
BitPagos Payments Gateway for Latin America
Coinbase Offers payment buttons, pages, iframes, shopping cart integration, subscription/recurring billing, micro-transactions, and cash out to your local currency for 1%.
Paysius Allows merchants to easily and securely accept Bitcoin payments on their website
Fasterco.in Bitcoin payment processing for merchants and day-traders
In-store Transactions
Shopping Cart Interfaces
Securing online services
Bitcoin Evolution handles sales tracking and order forms; requires Bitcoin client for actual payment
Bitcoin API Services an easy solution for securely accepting Bitcoins and updating BTC prices
Bitcoin Javascript Converter displays a price in BTCs after converting from USDs.
How to accept Bitcoin, for small businesses
Marketing
URI Scheme
Promotional graphics, buttons and logos
Lazy API The lazy (and possibly easiest?) way to accept bitcoin payments on your website
Snowcron Bitcoin Store Engine: Handles payments, sends your customers information they ordered (reg. codes, passwords...) No web programming required."
SOURCE:
https://en.bitcoin.it/wiki/Merchant_Howto <--- I highly recommend that you check this page
https://bips.me/
https://www.casinowebscripts.com/how-to-open-bitcoin-casino.htmlHope they may be of some help to finding what you're looking for.