Where can I get a SCSI to USB or Firewire to USB adapter.

Welcome Joe

With a "where" question, can you give us a rough idea of where you are geographically? These are truly international forums and we would do you a disservice to recommend a vendor who cannot or will not ship to your location.

It may also help to more precisely identify the legacy storage devices and the device to which your wish to connect them. That is in the event something brand- or type-specific is involved. Remember there are both FireWire 400 and FW 800 devices, each with unique connectors. More info is always good!

There are also FW400/FW800 cables and adapters so if the only Firewire to USB adapter is not the version Firewire needed, it should be easy to get the appropriate adapter, either 400 to 800 or 800 to 400.

NE Pa.

Excellent. Thanks, Joe.

Other World Computing is my first stop for odd Mac needs. I'd start here (this link should return search results for "cables"):

Apple Mac Upgrades - RAM, SSD Flash, External Drives and More

Try other search strings if needed. Newegg has also been useful for odd cabling.

SCSI may be harder. Is it the MO drive that is SCSI? What computer are you connecting to? At least with Apple, their progressive deprecation of what they consider legacy ports has made it hard to guess what ports are still available without knowing the sub-model. "iMac" is too broad but "Late 2012" iMac is spot-on for our learning what ports you have available for the project.

Ditto on OWC. Question what type of connection is on the hard drive itself in the LaCie Porsche external drive? If it is an ATA, IDE or ATAPI, then this kit should help: NewerTech Universal Drive Adapter USB Bare Drive... at MacSales.com