I was looking around the documentation for the AD8304 chip, and I was wondering if it has files to work with Altium Designer or SPICE (particularly I use LTSPICE over ORCAD for the time being). I cannot find any, so I was wondering if I could be directed to where they may be and/or submit a request to have these be created. I know that Analog Devices typically is pretty good about having listings for their parts in these areas so I was a little surprised to not find them.
You might try the Ultra Librarian tool. Links to it appear on the AD8304 product page. Click the link "Design Resources" up at the top of the page. Under that, you will see a "Symbols and Footprints" link. Ultra Librarian claims to export to a number of popular CAD file formats. We do recommend you check the schematic and PCB pad footprints for basic accuracy, as these tools can make mistakes, just like people.
AD8304 LTspice model files are planned to be available within the next few months. These updates will roll out automatically within the weekly LTspice updates.