Are there enzymes for every given reaction?
This will probably be a difficult question to answer definitively without some hand-waving or redefining the question; I can't imagine proving the negative result that no enzyme is possible for a given reaction, except for some cases where the reaction is just thermodynamically impossible outside of incredible conditions (for an extreme example, what about hydrogen fusion: the reaction exists, but the conditions necessary are outside the tolerance of protein-based catalysts). 

As @tomd pointed out in a comment, enzymes do not change equilibrium, so enzymes are only possible for reactions that are thermodynamically favorable. However, some enzymes couple reactions that are thermodynamically unfavorable with highly favorable reactions to produce a net thermodynamically favorable reaction, which greatly increases the number of reactions that can theoretically be catalyzed.

As for whether any shape can be created out of polypeptides: given the diversity of amino acids and the structural effects of the tertiary structure of proteins, there is a near limitless array of combinations which exceeds human comprehension, but not a truly mathematically infinite number. There are interesting projects such as this one that seek to harnessed underutilized computing power to iterate all of these possibilities to search for useful drugs and explain the causes of disease.