In these cases it is pretty straight forward. A 21st birthday usually entails the giving of a key, a 25th wedding anniversary is marked by the giving of silver as it is a silver anniversary, a 50th year of marriage is a golden wedding anniversary and so on.
Although these are some examples of the best known landmarks in life, some years are also marked in a special way with gifts representing this notable occasion. The first year of marriage is known as a paper anniversary, so gifts containing paper are often exchanged and the 5th year of a married couples' time together is known as a wooden anniversary.
Despite all these landmark occasions and dates, often created by greetings card companies and gift shops, it appears there is no special gift for a 61st anniversary. The nearest which does have a designated gift is the 60th, which is known as the diamond wedding anniversary.
It may be better to create your own gift idea for your partner, maybe make something or write a poem that expresses how you feel. This is a more unique and personal way of showing your feelings on this special day.