For the cassock it is probably best if you buy the fabric and have someone make it for you. That way it would really fit your measurements.

For the surplice I got mine from Amazon, here is one, for example: https://www.amazon.com/Pleated-Surplice-Length-Sleeve-5ft6-5ft9/dp/B00E6AG2H0/ref=sr\_1\_3?crid=2GMKCV7ASB3T5&keywords=surplice&qid=1675686897&sprefix=surplic%2Caps%2C143&sr=8-3