According to English Silver Coins by P. Alan Rayner the young head crowns are common in worn to average condition but are very difficult to obtain EF.
The rarity of an uncirculated specimen would perhaps be R3. The item "Great Britain 1845 Victoria Silver Crown NGC MS-62 Colorful iridescent tone" is in sale since Monday, July 27, 2020. This item is in the category "Coins & Paper Money\Coins\ World\Europe\UK (Great Britain)\Crown".
The seller is "vdukat" and is located in Feasterville-Trevose, Pennsylvania. This item can be shipped worldwide.