In order to clean up the lazarus installation the few rx components in the folder (lazarus)/components/rx were merged with the comprehensive rx component set on Lazarus Code and Components Repository (CCR). They now can be found in
https://sourceforge.net/p/lazarus-ccr/svn/HEAD/tree/components/rx/trunk/rx_laz/. The package file, rx.lpk, is located one level higher along with the other lpk files.
After some grace period, the folder (lazarus)/components/rx will be deleted from Lazarus trunk.