Amazon.com: USB Port Converter Module USB Converter Module Serial Parallel to UART IIC SPI TTL ISP EPP MEM Components CH341A : Electronics
USB SPI click - Breakout board for MCP2210 USB to SPI converter
Buy FT232H - USB converter for UART, SPI, I2C Botland - Robotic Shop
Adafruit FT232H Breakout - General Purpose USB to GPIO, SPI, I2C [USB C & Stemma QT] : ID 2264 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Simply add USB to your design with bridge devices from Silicon Labs
SPI Multiplexing IC" and "USB-SPI Bridge IC" recommended - Switches & multiplexers forum - Switches & multiplexers - TI E2E support forums
USB SPI Slave Breakout Board from Earth People Technology on Tindie
Devantech USB to UART, I2C, SPI, serial adapter (USB-ISS) | Acroname
Page 2 | USB-SPI Adapters
CH341 USB To UART, I2C, SPI Parallel Breakout Board - ElectroDragon
UMFT4222EV-D FTDI, Future Technology Devices International Ltd | Development Boards, Kits, Programmers | DigiKey