What IR sensor are you using? What Ultrasonic sensor are you using? What Accelerometer are you using? Are they analog or digital devices? Are they I2C or Serial devices?

Check for a datasheet on each of these sensors from their manufacturer. It will tell you how many volts they can support. It will tell you which plug is +, - and signal. If they are I2C or Serial, you will need different cables but I2C cables are sold in the store. From there start looking in the LEARN section of this site, specifically this page https://synthiam.com/Tutorials/Lesson/72?courseId=4

Digital ports are not power regulated on the EZ-B robot controller. This means that the voltage from the digital pins are 7.4 Volts on the JD robot. You might need to regulate power to the devices depending on if they already include voltage regulation.

As far as getting specific plastics, it is possible to 3D print cases and parts from this site, or purchase the parts you request for the most part. The IR sensor and Accelerometer don't have plastics designed for them. You can use many free software products to design parts for 3D printing. There is a 3D printing community here with people who may print the parts for you at a cost.

Really, there is an extreme amount of missing information here for anyone to be of much help to you.

Thanks.