"Find someone to take you for a fast walk" 或者 "Find someone to take you on a fast walk" 都是正确的表达方式。
"Fast walk" 指的是快走，这是一个常见的英文表达方式，意思是走得比慢走快一些，但比跑步慢得多。
下面是一些例句：
I'm going for a fast walk around the neighborhood before dinner.
(我会在晚餐前在附近快走一圈。)
Do you want to join me for a fast walk in the park?
(你想和我一起在公园里快走吗？)
I try to take a fast walk every day to get some exercise.
(我每天都会快走一会儿以便锻炼身体。)