ArduSimple are in Andorra and Spain, and are primarily focuses on the RTK case. They make an M.2 card with antenna and time pulse out connectors that can fit in a wifi M.2 slot in a PC.
Beitian are a Chinese company that make a range of GNSS boards, modules and antennas. They have their own direct store, but I have bought through AliExpress.
BG7TBL is a rather mysterious Chinese vendor. The nearest to an official website is their Taobao store. They make some nice external GNSS units. They also make an antenna splitter.
FS make some inexpensive switches with PTP support.
gnss.store are in Latvia. They make some USB dongle with SMA connectors for antenna and time pulse out.
SparkFun Electronics make a variety of GNSS boards. I haven’t used them much because their US location is not convenient for me.
Star River is a Chinese company that make a number of GNSS boards that are inexpensive and work well in a CM4/5.
They have stores on AliExpress and on Taobao. The Taobao shop seems to have a wider range.
Time Appliances make the TimeHAT, which is a hat for a Raspberry Pi 5, with an Intel i226 NIC.
TimeBeat are in London, UK. They make a board for the CM4/5 in a unique “sandwich” form factor.
Waveshare are in China. Amongst other things, they make some carrier boards and cases for the CM4/5.
Distributors
AliExpress is a China-based marketplace intended for buyers outside China. It is important to understand that AliExpress does not sell products itself. It is a platform that connects buyers and sellers. The key thing is to choose the seller the carefully. They have ratings out of 5, but it’s best to ignore the leading 4 and treat it as a rating out of 10, i.e. consider a seller with a rating of 4.5 as having a rating of 5/10. I have bought a lot from AliExpress, and my experiences have overall been very good. Shipping times can be long.
DigiKey is a large US-based electronics distributor. They are a good source for u-blox EVKs.
eBay have a lot of resellers of Chinese-made products. It can be a little less daunting for a Western buyer than AliExpress or Taobao, although the prices can be higher.
Mouser Electronic is another large US-based electronics distributor. I have had slightly better experience with Digi-Key.
Taobao is a China-based marketplace. It is primarily designed for residents of China, but they can ship direct to some countries outside China in the Asia-Pacific region. If you don’t live in one of these countries, it’s a bit of a challenge to use (Google translate helps a lot), but it is possible. I have found the vendors to be generally honest. As with AliExpress, you need to carefully choose which stores you buy from. Shipping times tend to be long.
Tindie is a US-based market place for small electronics vendors.