You can easily get to GPIO #0 #1 and #2 using large alligator clips. With a microbit breakout, you can access the other 16 or so.

Note that many of these pins are multiplexed with the LED matrix so if you decide to use that, you can't use them for analog inputs or digital I/O

• Pin #0 - large pad - analog in
• Pin #1 - large pad - analog in
• Pin #2 - large pad - analog in
• Pin #3 - analog in, also used for LED matrix
• Pin #4 - analog in, also used for LED matrix
• Pin #5 - also used for Button A
• Pin #6 - also used for LED matrix
• Pin #7 - also used for LED matrix
• Pin #8
• Pin #9 - also used for LED matrix
• Pin #10 - analog in, also used for LED matrix
• Pin #11 - also used for button B
• Pin #12
• Pin #13 - also available as SPI clock
• Pin #14 - also available as SPI MISO
• Pin #15 - also available as SPI MOSI
• Pin #16
• Pin #19 - also available as I2C clock
• Pin #20 - also available as I2C data

So really, if you're using the buttons and LEDs, you can use pins: #0, #1, #2, #8, #12, #13, #14, #15, #16, #19 and #20. Which is still a good amount!

blynk.cc has a great graphic of the pin mapping to Arduino IDE: