Find first unique occurance of match in file using regex

Question

I would like to find the first unique occurrence of a match within a file. In the example data below, I would like to find the first occurrence of each Chunk

Chunk 1
some text
second line of random text
Chunk 2
some text
second line of random text
Chunk 3
some text
second line of random text
Chunk 1
some text
second line of random text
Chunk 3
some text
second line of random text
Chunk 2
some text
second line of random text

Chunks[1-8], will return all the instances of the matches, I just want the first time each unique Chunk number is listed. Regex will work, so I can use in Notepad++ and eventually incorporate into a python script. I'd also like to return the unique match, along with the "second line of random text" after each unique match

So what I would like to see is

Chunk 1 (first occurrence)
second line of random text
Chunk 2 (first occurrence)
second line of random text<br>
Chunk 3 (first occurrence)
second line of random text

Answer 1

With GNU awk:

gawk -v 'RS=Chunk [0-9]+\n' -v ORS= '
  {$0=lastRT $0}
  NR>1 && !seen[$0]++
  {lastRT = RT}'

Answer 2

With perl. Not particularly readable, awk approach far better.

perl -ne 'if(/^Chunk [0-9]+$/&&!exists($seen{$_})){$seen{$_}++;chomp;$a=$_;$_=<>;$_=<>;print "$a $_"}'