Did you not read the earlier comments where Martin went on a rant about no one asking Oswald about where he purchased the pistol?
You keep quoting Mae Brussell's invented dialog. Here's what Fritz's report actually said:
"I asked him again why he carried the pistol to the show. He refused to answer questions about the pistol. He did tell me, however, that he had bought it several months before in Fort Worth, Texas."
There's nothing in there about Oswald refusing to tell Fritz where in Fort Worth the pistol was purchased. Or of Fritz even asking him that.