Electronic – Clarification regarding I2C address

Your problem can be solved with SMBus which is logically an extension on I2C. SMBus supports an ARP, wherein it can detect multiple IC's of same address, and assign them a different address. The ARP process basically reads a UUID ( a unique id per device; all the different devices in the same lot will have a different UUID) from the slave address (there may be multiple devices on this slave address). Due to the I2C bus arbiration process, only one slave will succeed at a time, and the master successfully reads its UUID. Then the master assigns a unique address using that UUID as reference. The process is repeated until all the slaves get a resolved address.

The accelerometer address is 0x1D by default and can be changed to 0x1C with a bit of soldering(Found in the Address Select Jumper section of the guide you linked). The gyroscope address is 0x69 by default and can be changed to 0x68(Found in section 6.1.1 of the datasheet, and the I2C Address Jumper section of the guide you linked). The Arduino can theoretically support as many I2C devices as can be acquired without having two that share an address.

Note also that accelerometers and gyroscopes are often packaged together on a single chip, which may be easier to work with. I've used the MPU-9150 with good results.