I wonder if you mean similes rather than metaphors? The two are easily confused. I have checked the section that you refer to and cannot find any metaphors, but there are two obvious similes. Let us remember the difference between them. Metaphors and similes are both comparisons that are asserted between two objects that are very different that help us to see how they are linked. However, similes include the words "like" or "as" whereas metaphors do not.

The two examples of similes in this selection therefore are:

Say thou wilt course, thy greyhounds are as swift
As breathed stags, ay, fleeter than the roe.

And:

And till the tears that she hath shed for thee
Like envious floods o'errun her lovely face...

The first simile is used to describe the greyhounds that Sly supposedly has in his "new" state of being a Lord. Note how the comparison emphasises their speed by comparing them to "breathed stags" and a "roe." The second simile talks about the grief of Sly's supposed wife that she has expressed for him, using hyperbole to exaggerate her grief by comparing her tears to "envious floods." This scene and the language contained therein is all designed to trick Sly into believing that he is a Lord.