comma's

I know you posted this a long time ago, this is my suggestion. Your sentence has two complete clauses--a subject, a verb, and an object--however it lacks a coordinating conjunction, which would join the clauses together. I would use 'yet'--see below:  

"I was hoping to find time today, yet I didn't find any."

'However' is not one of these conjunctions, if it was we could just use a comma. In order to show the same kind of relationship between the two clauses, use a semicolon before your transitional expression. Here's the example below:

I was hoping to find time today; however, I didn't find any.  

As a general rule always use a semicolon before a transitional expression, such as 'however.'

See below:

Complete Sentence (; transitional expression) Complete Sentence

                                  ; however,
                                  ; in fact,
                                  ; moreover,
                                  ; furthermore,
                                  ; therefore,

If you need me to clarify anything, please let me know.