In case this is useful to others, here's some code I've been using to
find all senders of message within a given category. 
It's implemented on SystemDictionary.

browseCallsOn: aLiteral category: aCategory
	"Show all senders of aLiteral in classes with category prefix aCategory"
	"Smalltalk browseCallsOn: #fork category: 'OSProcess'."
	"This omits some refinements as seen in, e.g.,  #allCallsOn:"
	|myClasses  myMethods|

	myClasses := OrderedCollection new.
	(Utilities classCategoriesStartingWith: aCategory) do: [:cat |
		myClasses addAll: (SystemOrganization listAtCategoryNamed: cat).
		].
	myClasses := myClasses collect: [:c | self classNamed: c].
	myClasses addAll: (myClasses collect: [:c | c class "we want class methods as well as instance methods"]).
	myMethods := OrderedCollection new.
	myClasses do: [:myClass |
		( myClass whichSelectorsReferTo: aLiteral) do: [:sel |
			myMethods add: (
				MethodReference new
					setStandardClass: myClass
					methodSymbol: sel
				).
			].
		].
	self browseMessageList: myMethods 
		name: 'senders of ', aLiteral asString, ' in ',  aCategory asString, ' package'
		autoSelect: aLiteral.
		
	

	
I ran this in Cuis 2.6, though I think it should work in other images.
Note that Cuis lacks PackageInfo, which Levente Uzonyi used in a
2010-04-12 posting that provides something similar in spirit.

I suspect this is too special purpose to be added to the standard image.
If you use it in a workspace or as a method off Utilies, change self to
Smalltalk.

Comments welcome.

Ross Boylan