I only access the Citrix Website from time to time so I am always searching for the download page of the Netscaler VPX Express Edition. If you need it too you can find it under the following URL:
You need a Citrix account to access this site.
You can also navigate there from the regular download page via https://www.citrix.com/downloads -> “Select a product: Netscaler ADC” -> “Netscaler VPX Express”. Please note that there is no 12.x Netscaler VPX Express Edition. Only the 11.x branch is available.