Where to get NT Modules
The list of vendors below is collected solely for your convenience! It is NOT an official seller list, nor implies any recommendation. The list may not be complete, the order of vendors is arbitrary, and vendors not mentioned are equally trustworthy.
Gapey NT Modules
Gapey provides a broad selection of NT modules, including NT IMU modules, NT Motor-Encoder modules, and NT Logger modules, as well as boards such as the ESP8266 adapter or OLED Display module. Gapey's modules are largely based on the original designs, with few modifications here and where, and work with the official firmwares. For further details, please visit the web page.
ENSYS NT Modules
ENSYS provides a selection of proprietary NT modules, including NT IMU modules, NT Motor modules, a wifi NT Logger module, or a NT Led-Battery module. The ENSYS NT modules are mostly based on a LPC1111 micro controller, and use propietary firmwares. For further details, please visit their web page.
STorM32 v1.3 board with NT IMU module: Where to buy STorM32 boards
Comment: The widely available OpenLog data logger and its many derivatives, which have become popular with Beta/Clean/Race/etc-Flight, cannot be used. In fact, to the best of the firmware author's knowledge, none of the available data loggers can be used. So, if you find a logger then assume it doesn't work, unless it is specifically declared as NT logger.
The Open Pilot CC3D Atom can be used as NT IMU module, when flashed with the respective NT firmware. With the pin headers stripped off, it is also relatively small.
The Mini CC3D is even smaller, without the need of hardware modifications. Unfortunately it can only be first-time flashed via SWD, and a ST-Link programmer is additionally needed for converting it into a NT IMU module.
Both boards are available cheaply from various Asian sources, and of course also at somewhat higher prices in many "regular" shops.
Cables and Connectors
Unfortunately I don't know about a cheap and readily available source of suitable pre-configured cables with plugs. The 1 mm JST-SH connector has however become kind of a standard in the RC world, and used for e.g. flight controllers, gimbal controllers, etc., which gives options.